Happy Codings - Programming Code Examples
Html Css Web Design Sample Codes CPlusPlus Programming Sample Codes JavaScript Programming Sample Codes C Programming Sample Codes CSharp Programming Sample Codes Java Programming Sample Codes Php Programming Sample Codes Visual Basic Programming Sample Codes


C Programming Code Examples

C > Gnu-Linux Code Examples

Convert a time value to and from UTC time

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105
/* Convert a time value to and from UTC time */ #include <stdio.h> #include <getopt.h> #include <string.h> #include <stdlib.h> #include <unistd.h> /* strptime() */ #define __USE_XOPEN #include <time.h> #define PACKAGE "utconv" #define VERSION "0.0.1" void print_help(int exval); /* status epilepticus, print help */ int get_utc(char *str); /* extract UTC time from string */ char *convert_utc(int uval); /* convert UTC to time string */ int main(int argc, char *argv[]) { int opt = 0; if(argc == 1) print_help(0); while((opt = getopt(argc, argv, "hvu:s:")) != -1) { switch(opt) { case 'h': /* print help and exit */ print_help(0); break; case 'v': /* print version and exit */ fprintf(stdout, "%s %s\n", PACKAGE, VERSION); exit(0); break; case 'u': /* convert INT utc value to timestring */ printf("%s\n", convert_utc(atoi(optarg))); break; case 's': /* convert STR to INT utc time value */ /* small check for correct user input ... */ if(strlen(optarg) < 23 || strlen(optarg) > 24) { fprintf(stderr, "%s: Error, correct format ? `%s'\n", PACKAGE, optarg); fprintf(stderr, "%s: Something like this maybe: `Sun Sep 7 00:00:04 2003'\n\n", PACKAGE); return 1; } printf("%d\n", get_utc(optarg)); break; case '?': fprintf(stderr, "%s: Error - No such option `%c'\n", PACKAGE, optopt); print_help(1); case ':': fprintf(stderr, "%s: Error - Option `%c' requires an argument\n", PACKAGE, optopt); print_help(1); } /* switch */ } /* while */ return 0; } /* convert INT UTC to time string */ char *convert_utc(int uval) { time_t timeval; char *tstr = NULL; timeval = uval; tstr = strdup(ctime(&timeval)); /* remove trailing newline */ tstr[strlen(tstr) - 1] = '\0'; return tstr; free(tstr); } int get_utc(char *str) { struct tm timestruct; int retval = 0; /* Sun Sep 7 00:00:04 2003 */ if(strptime(str, "%a %b %d %T %Ey", ×truct) == 0) return -1; else { timestruct.tm_year -= 1900; timestruct.tm_isdst = -1; } retval = mktime(×truct); return retval; } /* print help, status epilepticus */ void print_help(int exval) { printf("%s,%s convert a time value to and from UTC time\n", PACKAGE, VERSION); printf("Usage: %s [-h] [-v] [-s STR] [-u INT]\n\n", PACKAGE); printf(" -h print this help and exit\n"); printf(" -v print version info and exit\n\n"); printf(" -u INT convert UTC time `INT' to a human readable format\n"); printf(" -s STR convert time `STRING' to an UTC value\n"); printf(" format of `STR' should be:\n"); printf(" Sun Sep 7 00:00:04 2003\n\n"); exit(exval); }
free() Function in C
The free() function in C library allows you to release or deallocate the memory blocks which are previously allocated by calloc(), malloc() or realloc() functions. It frees up the memory blocks and returns the memory to heap. It helps freeing the memory in your program which will be available for later use. In C, the memory for variables is automatically deallocated at compile time. For dynamic memory allocation in C, you have to deallocate the memory explicitly. If not done, you may encounter out of memory error.
Syntax for free() Function in C
#include<stdlib.h> void free(void *ptr).
ptr
This is the pointer to a memory block previously allocated with malloc, calloc or realloc to be deallocated. If a null pointer is passed as argument, no action occurs. This function does not return any value.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
/* deallocate memory block by free() function example */ #include <stdio.h> #include <stdlib.h> #include <string.h> int main () { char *str; /* Initial memory allocation */ str = (char *) malloc(15); strcpy(str, "HappyCodings"); printf("String = %s, Address = %u\n", str, str); /* Reallocating memory */ str = (char *) realloc(str, 25); strcat(str, ".com"); printf("String = %s, Address = %u\n", str, str); /* Deallocate allocated memory */ free(str); return(0); }
#define Directive in C
In the C Programming Language, the #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. Macro definitions are not variables and cannot be changed by your program code like variables. You generally use this syntax when creating constants that represent numbers, strings or expressions.
Syntax for #define Directive in C
#define NAME value /* this syntax creates a constant using define*/ // Or #define NAME (expression) /* this syntax creates a constant using define*/
NAME
is the name of a particular constant. It can either be defined in smaller case or upper case or both. Most of the developers prefer the constant names to be in the upper case to find the differences.
value
defines the value of the constant.
Expression
is the value that is assigned to that constant which is defined. The expression should always be enclosed within the brackets if it has any operators. In the C programming language, the preprocessor directive acts an important role within which the #define directive is present that is used to define the constant or the micro substitution. The #define directive can use any of the basic data types present in the C standard. The #define preprocessor directive lets a programmer or a developer define the macros within the source code. This macro definition will allow the constant value that should be declared for the usage. Macro definitions cannot be changed within the program's code as one does with other variables, as macros are not variables. The #define is usually used in syntax that created a constant that is used to represent numbers, strings, or other expressions. The #define directive should not be enclosed with the semicolon(;). It is a common mistake done, and one should always treat this directive as any other header file. Enclosing it with a semicolon will generate an error. The #define creates a macro, which is in association with an identifier or is parameterized identifier along with a token string. After the macro is defined, then the compiler can substitute the token string for each occurrence of the identifier within the source file.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29
/* #define directive allows the definition of macros within your source code. These macro definitions allow constant values to be declared for use throughout your code. */ #include <stdio.h> #include <string.h> typedef struct Books { char title[50]; char author[50]; char subject[100]; int book_id; } Book; int main( ) { Book book; strcpy( book.title, "C Programming"); strcpy( book.author, "XCoder"); strcpy( book.subject, "C Programming Tutorial"); book.book_id = 6495407; printf( "Book title : %s\n", book.title); printf( "Book author : %s\n", book.author); printf( "Book subject : %s\n", book.subject); printf( "Book book_id : %d\n", book.book_id); return 0; }
While Loop Statement in C
While loop is also known as a pre-tested loop. In general, a while loop allows a part of the code to be executed multiple times depending upon a given boolean condition. It can be viewed as a repeating if statement. The while loop is mostly used in the case where the number of iterations is not known in advance. The while loop evaluates the test expression inside the parentheses (). If test expression is true, statements inside the body of while loop are executed. Then, test expression is evaluated again. The process goes on until test expression is evaluated to false. If test expression is false, the loop terminates.
Syntax of While Loop Statement in C
while (testExpression) { // the body of the loop }
• The while loop evaluates the testExpression inside the parentheses (). • If testExpression is true, statements inside the body of while loop are executed. Then, testExpression is evaluated again. • The process goes on until testExpression is evaluated to false. • If testExpression is false, the loop terminates (ends).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
/* while loop statement in C language */ #include<stdio.h> int main() { int n, num, sum = 0, remainder; printf("Enter a number: "); scanf("%d", &n); num = n; // keep looping while n > 0 while( n > 0 ) { remainder = n % 10; // get the last digit of n sum += remainder; // add the remainder to the sum n /= 10; // remove the last digit from n } printf("Sum of digits of %d is %d", num, sum); // signal to operating system everything works fine return 0; }
exit() Function in C
The exit() function is used to terminate a process or function calling immediately in the program. It means any open file or function belonging to the process is closed immediately as the exit() function occurred in the program. The exit() function is the standard library function of the C, which is defined in the stdlib.h header file. So, we can say it is the function that forcefully terminates the current program and transfers the control to the operating system to exit the program. The exit(0) function determines the program terminates without any error message, and then the exit(1) function determines the program forcefully terminates the execution process.
Syntax for exit() Function in C
#include <stdlib.h> void exit(int status)
status
Status code. If this is 0 or EXIT_SUCCESS, it indicates success. If it is EXIT_FAILURE, it indicates failure. The exit function does not return anything. • We must include the stdlib.h header file while using the exit () function. • It is used to terminate the normal execution of the program while encountered the exit () function. • The exit () function calls the registered atexit() function in the reverse order of their registration. • We can use the exit() function to flush or clean all open stream data like read or write with unwritten buffered data. • It closed all opened files linked with a parent or another function or file and can remove all files created by the tmpfile function. • The program's behaviour is undefined if the user calls the exit function more than one time or calls the exit and quick_exit function. • The exit function is categorized into two parts: exit(0) and exit(1).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
/* call all functions registered with atexit and terminates the program by exit() function example */ #include <stdio.h> #include <stdlib.h> int main () { // declaration of the variables int i, num; printf ( " Enter the last number: "); scanf ( " %d", &num); for ( i = 1; i<num; i++) { // use if statement to check the condition if ( i == 6 ) /* use exit () statement with passing 0 argument to show termination of the program without any error message. */ exit(0); else printf (" \n Number is %d", i); } return 0; }
ctime() Function in C
Convert time_t value to string. Interprets the value pointed by timer as a calendar time and converts it to a C-string containing a human-readable version of the corresponding time and date, in terms of local time. The returned string has the following format: Www Mmm dd hh:mm:ss yyyy Where Www is the weekday, Mmm the month (in letters), dd the day of the month, hh:mm:ss the time, and yyyy the year. The string is followed by a new-line character ('\n') and terminated with a null-character. This function is equivalent to: asctime(localtime(timer)) The C library function char *ctime(const time_t *timer) returns a string representing the localtime based on the argument timer. The returned string has the following format: Www Mmm dd hh:mm:ss yyyy, where Www is the weekday, Mmm the month in letters, dd the day of the month, hh:mm:ss the time, and yyyy the year. The ctime() function is define in the time.h header file. The ctime() function returns the string representing the localtime based on the argument timer.
Syntax for ctime() Function in C
#include <time.h> char *ctime(const time_t *timer)
timer
Pointer to an object of type time_t that contains a time value. time_t is an alias of a fundamental arithmetic type capable of representing times as returned by function time. A C-string containing the date and time information in a human-readable format. The returned value points to an internal array whose validity or value may be altered by any subsequent call to asctime or ctime.
Www
Day of week
Mmm
Month name
dd
Day of month
hh
Hour digit
mm
Minute digit
ss
Second digit
yyyy
Year digit
Data races
The function accesses the object pointed by timer. The function also accesses and modifies a shared internal buffer, which may cause data races on concurrent calls to asctime or ctime. Some libraries provide an alternative function that avoids this data race: ctime_r (non-portable).
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21
/* get the string representing the localtime based on the argument timer by ctime() function example */ #include <stdio.h> /* printf */ #include <time.h> /* time_t, time, ctime */ int main () { time_t rawtime; time (&rawtime); printf ("The current local time is: %s", ctime (&rawtime)); time (&rawtime); printf ("The current local time is: %s", ctime (&rawtime)); time (&rawtime); printf ("The current local time is: %s", ctime (&rawtime)); return 0; }
atoi() Function in C
Convert string to integer. Parses the C-string str interpreting its content as an integral number, which is returned as a value of type int. The function first discards as many whitespace characters (as in isspace) as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many base-10 digits as possible, and interprets them as a numerical value. The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function. If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed and zero is returned.
Syntax for atoi() Function in C
#include <stdlib.h> int atoi (const char * str);
str
C-string beginning with the representation of an integral number. The atoi() function converts a string of characters representing a numeral into a number of int. Similarly, atol() returns a long integer, and in C99, the atoll() function converts a string into an integer of type long long. The conversion ignores any leading whitespace characters (spaces, tabs, newlines). A leading plus sign is permissible; a minus sign makes the return value negative. Any character that cannot be interpreted as part of an integer, such as a decimal point or exponent sign, has the effect of terminating the numeral input, so that atoi() converts only the partial string to the left of that character. If under these conditions the string still does not appear to represent a numeral, then atoi() returns 0. On success, the function returns the converted integral number as an int value. If the converted value would be out of the range of representable values by an int, it causes undefined behavior. See strtol for a more robust cross-platform alternative when this is a possibility.
Data races
The array pointed by str is accessed.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
/* convert string to integer by atoi() function example */ #include <stdio.h> // Iterative function to implement `atoi()` function in C long atoi(const char* S) { long num = 0; int i = 0; // run till the end of the string is reached, or the // current character is non-numeric while (S[i] && (S[i] >= '0' && S[i] <= '9')) { num = num * 10 + (S[i] - '0'); i++; } return num; } // Implement `atoi()` function in C int main(void) { char S[] = "12345"; printf("%ld ", atoi(S)); return 0; }
If Else Statement in C
The if-else statement is used to perform two operations for a single condition. The if-else statement is an extension to the if statement using which, we can perform two different operations, i.e., one is for the correctness of that condition, and the other is for the incorrectness of the condition. Here, we must notice that if and else block cannot be executed simiulteneously. Using if-else statement is always preferable since it always invokes an otherwise case with every if condition.
Syntax for if-else Statement in C
if (test expression) { // run code if test expression is true } else { // run code if test expression is false }
If the test expression is evaluated to true, • statements inside the body of if are executed. • statements inside the body of else are skipped from execution. If the test expression is evaluated to false, • statements inside the body of else are executed • statements inside the body of if are skipped from execution.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
/* if else statement in C language */ // Check whether an integer is odd or even #include <stdio.h> int main() { int number; printf("Enter an integer: "); scanf("%d", &number); // True if the remainder is 0 if (number%2 == 0) { printf("%d is an even integer.",number); } else { printf("%d is an odd integer.",number); } return 0; }
printf() Function in C
Writes the C string pointed by format to the standard output (stdout). If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. printf format string refers to a control parameter used by a class of functions in the input/output libraries of C programming language. The string is written in a simple template language: characters are usually copied literally into the function's output, but format specifiers, which start with a % character, indicate the location and method to translate a piece of data (such as a number) to characters. "printf" is the name of one of the main C output functions, and stands for "print formatted". printf format strings are complementary to scanf format strings, which provide formatted input (parsing). In both cases these provide simple functionality and fixed format compared to more sophisticated and flexible template engines or parsers, but are sufficient for many purposes.
Syntax for printf() function in C
#include <stdio.h> int printf ( const char * format, ... );
format
C string that contains the text to be written to stdout. It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested. A format specifier follows this prototype: [see compatibility note below] %[flags][width][.precision][length]specifier Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
specifier
a conversion format specifier.
d or i
Signed decimal integer
u
Unsigned decimal integer
o
Unsigned octal
x
Unsigned hexadecimal integer
X
Unsigned hexadecimal integer (uppercase)
f
Decimal floating point, lowercase
F
Decimal floating point, uppercase
e
Scientific notation (mantissa/exponent), lowercase
E
Scientific notation (mantissa/exponent), uppercase
g
Use the shortest representation: %e or %f
G
Use the shortest representation: %E or %F
a
Hexadecimal floating point, lowercase
A
Hexadecimal floating point, uppercase
c
Character
s
String of characters
p
Pointer address
n
Nothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location.
%
A % followed by another % character will write a single % to the stream. The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:
flags
one or more flags that modifies the conversion behavior (optional)
-
Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+
Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space)
If no sign is going to be written, a blank space is inserted before the value.
#
Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero. Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0
Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
width
an optional * or integer value used to specify minimum width field.
(number)
Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*
The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
.precision
an optional field consisting of a . followed by * or integer or nothing to specify the precision.
.number
For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6). For g and G specifiers: This is the maximum number of significant digits to be printed. For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. If the period is specified without an explicit value for precision, 0 is assumed.
.*
The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
length
an optional length modifier that specifies the size of the argument.
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n). There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function. If a writing error occurs, the error indicator (ferror) is set and a negative number is returned. If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
/* print formatted data to stdout by printf() function example */ #include <stdio.h> int main() { char ch; char str[100]; int a; float b; printf("Enter any character \n"); scanf("%c", &ch); printf("Entered character is %c \n", ch); printf("Enter any string ( upto 100 character ) \n"); scanf("%s", &str); printf("Entered string is %s \n", str); printf("Enter integer and then a float: "); // Taking multiple inputs scanf("%d%f", &a, &b); printf("You entered %d and %f", a, b); return 0; }
strlen() Function in C
Get string length. Returns the length of the C string str. The length of a C string is determined by the terminating null-character: A C string is as long as the number of characters between the beginning of the string and the terminating null character (without including the terminating null character itself).
Syntax for strlen() Function in C
#include <string.h> size_t strlen ( const char * str );
str
C string Function returns the length of string. This should not be confused with the size of the array that holds the string. strlen() function is defined in string.h header file. It doesn't count null character '\0'.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
/* get the length of the C string str by strlen() function example */ /* Program to find the total length of a String using strlen() */ #include<stdio.h> #include<string.h> int main() { char str1[10]= "01234567"; /* First string */ printf("First String is %s",str1); printf("\n"); int length = strlen(str1); printf("Length of first String is %d", length); printf("\n"); char str2[20]= "String Chapter"; /* Second string */ printf("Second String is %s",str2); printf("\n"); length = strlen(str2); printf("Length of second String is %d", length); return 0; }
Switch Case Statement in C
Switch statement in C tests the value of a variable and compares it with multiple cases. Once the case match is found, a block of statements associated with that particular case is executed. Each case in a block of a switch has a different name/number which is referred to as an identifier. The value provided by the user is compared with all the cases inside the switch block until the match is found. If a case match is NOT found, then the default statement is executed, and the control goes out of the switch block.
Syntax for Switch Case Statement in C
switch(expression) { case constant-expression : statement(s); break; /* optional */ case constant-expression : statement(s); break; /* optional */ /* you can have any number of case statements */ default : /* Optional */ statement(s); }
• The expression used in a switch statement must have an integral or enumerated type, or be of a class type in which the class has a single conversion function to an integral or enumerated type. • You can have any number of case statements within a switch. Each case is followed by the value to be compared to and a colon. • The constant-expression for a case must be the same data type as the variable in the switch, and it must be a constant or a literal. • When the variable being switched on is equal to a case, the statements following that case will execute until a break statement is reached. • When a break statement is reached, the switch terminates, and the flow of control jumps to the next line following the switch statement. • Not every case needs to contain a break. If no break appears, the flow of control will fall through to subsequent cases until a break is reached. • A switch statement can have an optional default case, which must appear at the end of the switch. The default case can be used for performing a task when none of the cases is true. No break is needed in the default case.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39
/* switch case statement in C language*/ // Program to create a simple calculator #include <stdio.h> int main() { char operation; double n1, n2; printf("Enter an operator (+, -, *, /): "); scanf("%c", &operation); printf("Enter two operands: "); scanf("%lf %lf",&n1, &n2); switch(operation) { case '+': printf("%.1lf + %.1lf = %.1lf",n1, n2, n1+n2); break; case '-': printf("%.1lf - %.1lf = %.1lf",n1, n2, n1-n2); break; case '*': printf("%.1lf * %.1lf = %.1lf",n1, n2, n1*n2); break; case '/': printf("%.1lf / %.1lf = %.1lf",n1, n2, n1/n2); break; // operator doesn't match any case constant +, -, *, / default: printf("Error! operator is not correct"); } return 0; }
main() Function in C
In C, the "main" function is treated the same as every function, it has a return type (and in some cases accepts inputs via parameters). The only difference is that the main function is "called" by the operating system when the user runs the program. Thus the main function is always the first code executed when a program starts. main() function is a user defined, body of the function is defined by the programmer or we can say main() is programmer/user implemented function, whose prototype is predefined in the compiler. Hence we can say that main() in c programming is user defined as well as predefined because it's prototype is predefined. main() is a system (compiler) declared function whose defined by the user, which is invoked automatically by the operating system when program is being executed. Its first function or entry point of the program from where program start executed, program's execution starts from the main. So main is an important function in c , c++ programming language.
Syntax for main() Function in C
void main() { ......... // codes start from here ......... }
void
is a keyword in C language, void means nothing, whenever we use void as a function return type then that function nothing return. here main() function no return any value. In place of void we can also use int return type of main() function, at that time main() return integer type value.
main
is a name of function which is predefined function in C library. • An operating system always calls the main() function when a programmers or users execute their programming code. • It is responsible for starting and ends of the program. • It is a universally accepted keyword in programming language and cannot change its meaning and name. • A main() function is a user-defined function in C that means we can pass parameters to the main() function according to the requirement of a program. • A main() function is used to invoke the programming code at the run time, not at the compile time of a program. • A main() function is followed by opening and closing parenthesis brackets.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24
/* basic c program by main() function example */ #include <stdio.h> #include <conio.h> main() { printf (" It is a main() function "); int fun2(); // jump to void fun1() function printf ("\n Finally exit from the main() function. "); } void fun1() { printf (" It is a second function. "); printf (" Exit from the void fun1() function. "); } int fun2() { void fun1(); // jump to the int fun1() function printf (" It is a third function. "); printf (" Exit from the int fun2() function. "); return 0; }
fprintf() Function in C
Write formatted data to stream. Writes the C string pointed by format to the stream. If format includes format specifiers (subsequences beginning with %), the additional arguments following format are formatted and inserted in the resulting string replacing their respective specifiers. After the format parameter, the function expects at least as many additional arguments as specified by format.
Syntax for fprintf() Function in C
#include <stdio.h> int fprintf ( FILE * stream, const char * format, ... );
stream
Pointer to a FILE object that identifies an output stream.
format
C string that contains the text to be written to the stream. It can optionally contain embedded format specifiers that are replaced by the values specified in subsequent additional arguments and formatted as requested. A format specifier follows this prototype: %[flags][width][.precision][length]specifier Where the specifier character at the end is the most significant component, since it defines the type and the interpretation of its corresponding argument:
specifier
a conversion format specifier.
d or i
Signed decimal integer
u
Unsigned decimal integer
o
Unsigned octal
x
Unsigned hexadecimal integer
X
Unsigned hexadecimal integer (uppercase)
f
Decimal floating point, lowercase
F
Decimal floating point, uppercase
e
Scientific notation (mantissa/exponent), lowercase
E
Scientific notation (mantissa/exponent), uppercase
g
Use the shortest representation: %e or %f
G
Use the shortest representation: %E or %F
a
Hexadecimal floating point, lowercase
A
Hexadecimal floating point, uppercase
c
Character
s
String of characters
p
Pointer address
n
Nothing printed. The corresponding argument must be a pointer to a signed int. The number of characters written so far is stored in the pointed location.
%
A % followed by another % character will write a single % to the stream. The format specifier can also contain sub-specifiers: flags, width, .precision and modifiers (in that order), which are optional and follow these specifications:
flags
one or more flags that modifies the conversion behavior (optional)
-
Left-justify within the given field width; Right justification is the default (see width sub-specifier).
+
Forces to preceed the result with a plus or minus sign (+ or -) even for positive numbers. By default, only negative numbers are preceded with a - sign.
(space)
If no sign is going to be written, a blank space is inserted before the value.
#
Used with o, x or X specifiers the value is preceeded with 0, 0x or 0X respectively for values different than zero. Used with a, A, e, E, f, F, g or G it forces the written output to contain a decimal point even if no more digits follow. By default, if no digits follow, no decimal point is written.
0
Left-pads the number with zeroes (0) instead of spaces when padding is specified (see width sub-specifier).
width
an optional * or integer value used to specify minimum width field.
(number)
Minimum number of characters to be printed. If the value to be printed is shorter than this number, the result is padded with blank spaces. The value is not truncated even if the result is larger.
*
The width is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
.precision
an optional field consisting of a . followed by * or integer or nothing to specify the precision.
.number
For integer specifiers (d, i, o, u, x, X): precision specifies the minimum number of digits to be written. If the value to be written is shorter than this number, the result is padded with leading zeros. The value is not truncated even if the result is longer. A precision of 0 means that no character is written for the value 0. For a, A, e, E, f and F specifiers: this is the number of digits to be printed after the decimal point (by default, this is 6). For g and G specifiers: This is the maximum number of significant digits to be printed. For s: this is the maximum number of characters to be printed. By default all characters are printed until the ending null character is encountered. If the period is specified without an explicit value for precision, 0 is assumed.
.*
The precision is not specified in the format string, but as an additional integer value argument preceding the argument that has to be formatted.
length
an optional length modifier that specifies the size of the argument.
h
The argument is interpreted as a short int or unsigned short int (only applies to integer specifiers: i, d, o, u, x and X).
l
The argument is interpreted as a long int or unsigned long int for integer specifiers (i, d, o, u, x and X), and as a wide character or wide character string for specifiers c and s.
L
The argument is interpreted as a long double (only applies to floating point specifiers - e, E, f, g and G).
... (additional arguments)
Depending on the format string, the function may expect a sequence of additional arguments, each containing a value to be used to replace a format specifier in the format string (or a pointer to a storage location, for n). There should be at least as many of these arguments as the number of values specified in the format specifiers. Additional arguments are ignored by the function. On success, the total number of characters written is returned. If a writing error occurs, the error indicator (ferror) is set and a negative number is returned. If a multibyte character encoding error occurs while writing wide characters, errno is set to EILSEQ and a negative number is returned.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
/* write the C string pointed by format to the stream by fprintf() function example */ #include <stdio.h> void main() { FILE *fptr; int id; char name[30]; float salary; fptr = fopen("emp.txt", "w+");/* open for writing */ if (fptr == NULL) { printf("File does not exists \n"); return; } printf("Enter the id\n"); scanf("%d", &id); fprintf(fptr, "Id= %d\n", id); printf("Enter the name \n"); scanf("%s", name); fprintf(fptr, "Name= %s\n", name); printf("Enter the salary\n"); scanf("%f", &salary); fprintf(fptr, "Salary= %.2f\n", salary); fclose(fptr); }
Assignment Operators in C
Assignment operators are used to assign the value, variable and function to another variable. Assignment operators in C are some of the C Programming Operator, which are useful to assign the values to the declared variables. Let's discuss the various types of the assignment operators such as =, +=, -=, /=, *= and %=. The following table lists the assignment operators supported by the C language:
=
Simple assignment operator. Assigns values from right side operands to left side operand
+=
Add AND assignment operator. It adds the right operand to the left operand and assign the result to the left operand.
-=
Subtract AND assignment operator. It subtracts the right operand from the left operand and assigns the result to the left operand.
*=
Multiply AND assignment operator. It multiplies the right operand with the left operand and assigns the result to the left operand.
/=
Divide AND assignment operator. It divides the left operand with the right operand and assigns the result to the left operand.
%=
Modulus AND assignment operator. It takes modulus using two operands and assigns the result to the left operand.
<<=
Left shift AND assignment operator.
>>=
Right shift AND assignment operator.
&=
Bitwise AND assignment operator.
^=
Bitwise exclusive OR and assignment operator.
|=
Bitwise inclusive OR and assignment operator.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43
/* assignment operators in C language */ #include <stdio.h> main() { int a = 23; int c ; c = a; printf("Line 1 - = Operator Example, Value of c = %d\n", c ); c += a; printf("Line 2 - += Operator Example, Value of c = %d\n", c ); c -= a; printf("Line 3 - -= Operator Example, Value of c = %d\n", c ); c *= a; printf("Line 4 - *= Operator Example, Value of c = %d\n", c ); c /= a; printf("Line 5 - /= Operator Example, Value of c = %d\n", c ); c = 120; c %= a; printf("Line 6 - %= Operator Example, Value of c = %d\n", c ); c <<= 2; printf("Line 7 - <<= Operator Example, Value of c = %d\n", c ); c >>= 2; printf("Line 8 - >>= Operator Example, Value of c = %d\n", c ); c &= 2; printf("Line 9 - &= Operator Example, Value of c = %d\n", c ); c ^= 2; printf("Line 10 - ^= Operator Example, Value of c = %d\n", c ); c |= 2; printf("Line 11 - |= Operator Example, Value of c = %d\n", c ); }
mktime() Function in C
Convert tm structure to time_t. Returns the value of type time_t that represents the local time described by the tm structure pointed by timeptr (which may be modified). This function performs the reverse translation that localtime does. The values of the members tm_wday and tm_yday of timeptr are ignored, and the values of the other members are interpreted even if out of their valid ranges (see struct tm). For example, tm_mday may contain values above 31, which are interpreted accordingly as the days that follow the last day of the selected month. A call to this function automatically adjusts the values of the members of timeptr if they are off-range or -in the case of tm_wday and tm_yday- if they have values that do not match the date described by the other members.
Syntax for mktime() Function in C
#include <time.h> time_t mktime (struct tm * timeptr);
timeptr
Pointer to a tm structure that contains a calendar time broken down into its components (see struct tm).
struct tm { int tm_sec; /* seconds, range 0 to 59 */ int tm_min; /* minutes, range 0 to 59 */ int tm_hour; /* hours, range 0 to 23 */ int tm_mday; /* day of the month, range 1 to 31 */ int tm_mon; /* month, range 0 to 11 */ int tm_year; /* The number of years since 1900 */ int tm_wday; /* day of the week, range 0 to 6 */ int tm_yday; /* day in the year, range 0 to 365 */ int tm_isdst; /* daylight saving time */ };
A time_t value corresponding to the calendar time passed as argument. If the calendar time cannot be represented, a value of -1 is returned. The member tm_isdst is equal to 0 if daylight saving time is not in effect, or 1 if it is. A negative value indicates that the information is not available, in which case mktime() attempts to calculate whether daylight saving time is applicable at the time represented by the other members. The mktime() function ignores the tm_wday and tm_yday members in determining the time, but does use tm_isdst. The other members may contain values outside their normal ranges. Once it has calculated the time represented, mktime() adjusts the struct tm members so that each one is within its normal range, and also sets tm_wday and tm_yday accordingly. The return value is the number of seconds from the epoch (usually midnight on January 1, 1970, UTC) to the time represented in the structure, or -1 to indicate an error.
Data races
The object pointed by timeptr is accessed, and potentially modified.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36
/* determines the time represented by a struct tm value by mktime() function code example */ /* convert tm structure to time_t by mktime() function code example */ #include <stdio.h> #include <stdlib.h> #include <time.h> static const char *week_day[] = { "Sunday", "Monday", "Tuesday", "Wednesday", "Thursday", "Friday", "Saturday" }; int main( void ) { struct tm new_year; time_t t; new_year.tm_year = 2001 - 1900; new_year.tm_mon = 0; new_year.tm_mday = 1; new_year.tm_hour = 0; new_year.tm_min = 0; new_year.tm_sec = 0; new_year.tm_isdst = 0; t = mktime( &new_year ); if ( t == (time_t)-1) printf("No conversion possible.\n"); else printf( "The 21st century began on a %s.\n", week_day[ new_year.tm_wday ] ); return EXIT_SUCCESS; }
#include Directive in C
#include is a way of including a standard or user-defined file in the program and is mostly written at the beginning of any C/C++ program. This directive is read by the preprocessor and orders it to insert the content of a user-defined or system header file into the following program. These files are mainly imported from an outside source into the current program. The process of importing such files that might be system-defined or user-defined is known as File Inclusion. This type of preprocessor directive tells the compiler to include a file in the source code program. Here are the two types of file that can be included using #include: • Header File or Standard files: This is a file which contains C/C++ function declarations and macro definitions to be shared between several source files. Functions like the printf(), scanf(), cout, cin and various other input-output or other standard functions are contained within different header files. So to utilise those functions, the users need to import a few header files which define the required functions. • User-defined files: These files resembles the header files, except for the fact that they are written and defined by the user itself. This saves the user from writing a particular function multiple times. Once a user-defined file is written, it can be imported anywhere in the program using the #include preprocessor.
Syntax for #include Directive in C
#include "user-defined_file"
Including using " ": When using the double quotes(" "), the preprocessor access the current directory in which the source "header_file" is located. This type is mainly used to access any header files of the user's program or user-defined files.
#include <header_file>
Including using <>: While importing file using angular brackets(<>), the the preprocessor uses a predetermined directory path to access the file. It is mainly used to access system header files located in the standard system directories.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23
/* #include directive tells the preprocessor to insert the contents of another file into the source code at the point where the #include directive is found. */ // C program to illustrate file inclusion // <> used to import system header file #include <stdio.h> // " " used to import user-defined file #include "process.h" // main function int main() { // add function defined in process.h add(10, 20); // mult function defined in process.h multiply(10, 20); // printf defined in stdio.h printf("Process completed"); return 0; }
time() Function in C
The time() function is defined in time.h header file. This function returns the time since 00:00:00 UTC, January 1, 1970 (Unix timestamp) in seconds. If second is not a null pointer, the returned value is also stored in the object pointed to by second.
Syntax for time() Function in C
#include <time.h> time_t time( time_t *second )
second
This function accepts single parameter second. This parameter is used to set the time_t object which store the time. This function returns current calender time as a object of type time_t. It is used to get current system time as structure. time() function is a useful utility function that we can use to measure the elapsed time of our program.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
/* return the time since 00:00:00 UTC, January 1, 1970 by time() function example */ #include <time.h> #include <stdlib.h> #include <stdio.h> int main(void) { time_t current_time; char* c_time_string; /* Obtain current time. */ current_time = time(NULL); if (current_time == ((time_t)-1)) { (void) fprintf(stderr, "Failure to obtain the current time.\n"); exit(EXIT_FAILURE); } /* Convert to local time format. */ c_time_string = ctime(¤t_time); if (c_time_string == NULL) { (void) fprintf(stderr, "Failure to convert the current time.\n"); exit(EXIT_FAILURE); } /* Print to stdout. ctime() has already added a terminating newline character. */ (void) printf("Current time is %s", c_time_string); exit(EXIT_SUCCESS); }
Break Statement in C
The break is a keyword in C which is used to bring the program control out of the loop. The break statement is used inside loops or switch statement. The break statement breaks the loop one by one, i.e., in the case of nested loops, it breaks the inner loop first and then proceeds to outer loops.
Syntax for Break Statement in C
//loop statement... break;
When a break statement is encountered inside a loop, the loop is immediately terminated and the program control resumes at the next statement following the loop. It can be used to terminate a case in the switch statement (covered in the next chapter). If you are using nested loops, the break statement will stop the execution of the innermost loop and start executing the next line of code after the block.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
/* bring the program control out of the loop by break keyword */ // Program to calculate the sum of numbers (10 numbers max) // If the user enters a negative number, the loop terminates #include <stdio.h> int main() { int i; double number, sum = 0.0; for (i = 1; i <= 10; ++i) { printf("Enter n%d: ", i); scanf("%lf", &number); // if the user enters a negative number, break the loop if (number < 0.0) { break; } sum += number; // sum = sum + number; } printf("Sum = %.2lf", sum); return 0; }
getopt() Function in C
The getopt() function is a builtin function in C and is used to parse command line arguments. The getopt() function is a command-line parser that shall follow Utility Syntax Guidelines 3, 4, 5, 6, 7, 9, and 10 in the Base Definitions volume of IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guidelines. The parameters argc and argv are the argument count and argument array as passed to main() (see exec() ). The argument optstring is a string of recognized option characters; if a character is followed by a colon, the option takes an argument. All option characters allowed by Utility Syntax Guideline 3 are allowed in optstring. The implementation may accept other characters as an extension.
Syntax for getopt() Function in C
#include <unistd.h> int getopt(int argc, char * const argv[], const char *optstring); extern char *optarg; extern int optind, opterr, optopt;
argc
The argument count that was passed to main().
argv
The argument array that was passed to main().
optstring
A string of recognized option letters; if a letter is followed by a colon, the option takes an argument. Valid option characters for optstring consist of a single alphanumeric character (i.e. a letter or digit). The variable optind is the index of the next element of the argv[] vector to be processed. It shall be initialized to 1 by the system, and getopt() shall update it when it finishes with each element of argv[]. When an element of argv[] contains multiple option characters, it is unspecified how getopt() determines which options have already been processed. The getopt() function shall return the next option character (if one is found) from argv that matches a character in optstring, if there is one that matches. If the option takes an argument, getopt() shall set the variable optarg to point to the option-argument as follows: 1- If the option was the last character in the string pointed to by an element of argv, then optarg shall contain the next element of argv, and optind shall be incremented by 2. If the resulting value of optind is greater than argc, this indicates a missing option-argument, and getopt() shall return an error indication. 2- Otherwise, optarg shall point to the string following the option character in that element of argv, and optind shall be incremented by 1. If, when getopt() is called:
argv[optind] is a null pointer *argv[optind] is not the character - argv[optind] points to the string "-"
getopt() shall return -1 without changing optind. If:
argv[optind] points to the string "--"
getopt() shall return -1 after incrementing optind. If getopt() encounters an option character that is not contained in optstring, it shall return the question-mark ( '?' ) character. If it detects a missing option-argument, it shall return the colon character ( ':' ) if the first character of optstring was a colon, or a question-mark character ( '?' ) otherwise. In either case, getopt() shall set the variable optopt to the option character that caused the error. If the application has not set the variable opterr to 0 and the first character of optstring is not a colon, getopt() shall also print a diagnostic message to stderr in the format specified for the getopts utility. The getopt() function need not be reentrant. A function that is not required to be reentrant is not required to be thread-safe. The getopt() function shall return the next option character specified on the command line. A colon ( ':' ) shall be returned if getopt() detects a missing argument and the first character of optstring was a colon ( ':' ). A question mark ( '?' ) shall be returned if getopt() encounters an option character not in optstring or detects a missing argument and the first character of optstring was not a colon ( ':' ). Otherwise, getopt() shall return -1 when all command line options are parsed.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44
/* parse command line arguments by getopt() function code example */ // Program to illustrate the getopt() // function in C #include <stdio.h> #include <unistd.h> int main(int argc, char *argv[]) { int opt; // put ':' in the starting of the // string so that program can //distinguish between '?' and ':' while((opt = getopt(argc, argv, ":if:lrx")) != -1) { switch(opt) { case 'i': case 'l': case 'r': printf("option: %c\n", opt); break; case 'f': printf("filename: %s\n", optarg); break; case ':': printf("option needs a value\n"); break; case '?': printf("unknown option: %c\n", optopt); break; } } // optind is for the extra arguments // which are not parsed for(; optind < argc; optind++){ printf("extra arguments: %s\n", argv[optind]); } return 0; }
strdup() Function in C
Duplicate a specific number of bytes from a string. The strdup() function shall return a pointer to a new string, which is a duplicate of the string pointed to by str. The returned pointer can be passed to free(). A null pointer is returned if the new string cannot be created. The function strdup() is used to duplicate a string. It returns a pointer to null-terminated byte string. strdup reserves storage space for a copy of string by calling malloc. The string argument to this function is expected to contain a null character (\0) marking the end of the string.
Syntax for strdup() Function in C
#include <string.h> char* strdup( const char* str );
str
The string that you want to copy. The strdup() function shall return a pointer to a new string on success. Otherwise, it shall return a null pointer and set errno to indicate the error. Remember to free the storage reserved with the call to strdup. Strdup returns a pointer to the storage space containing the copied string. If it cannot reserve storage strdup returns NULL. strdup() function is non standard function which may not available in standard library in C.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20
/* duplicate a specific number of bytes from a string by strdup() string function code example */ // C program to demonstrate strdup() #include<stdio.h> #include<string.h> int main() { char source[] = "HappyCodings"; // A copy of source is created dynamically // and pointer to copy is returned. char* target = strdup(source); printf("%s", target); return 0; }
Logical Operators in C
An expression containing logical operator returns either 0 or 1 depending upon whether expression results true or false. Logical operators are commonly used in decision making in C programming. These operators are used to perform logical operations and used with conditional statements like C if-else statements.
&&
Called Logical AND operator. If both the operands are non-zero, then the condition becomes true.
||
Called Logical OR Operator. If any of the two operands is non-zero, then the condition becomes true.
!
Called Logical NOT Operator. It is used to reverse the logical state of its operand. If a condition is true, then Logical NOT operator will make it false.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33
/* logical operators in C language */ #include <stdio.h> main() { int a = 4; int b = 23; int c ; if ( a && b ) { printf("Line 1 - Condition is true\n" ); } if ( a || b ) { printf("Line 2 - Condition is true\n" ); } /* lets change the value of a and b */ a = 2; b = 8; if ( a && b ) { printf("Line 3 - Condition is true\n" ); } else { printf("Line 3 - Condition is not true\n" ); } if ( !(a && b) ) { printf("Line 4 - Condition is true\n" ); } }
strptime() Function in C
The strptime() function converts the character string pointed to by buf to values that are stored in the tm structure pointed to by tm, using the format specified by format. The format contains zero or more directives. A directive contains either an ordinary character (not % or a white space), or a conversion specification. Each conversion specification is composed of a % character followed by one or more conversion characters, which specify the replacement required. There must be a white space or other delimiter in both buf and format to be guaranteed that the function will behave as expected. There must be a delimiter between two string-to-number conversions, or the first number conversion may convert characters that belong to the second conversion specifier.
Syntax for strptime() Function in C
#include <time.h> char *strptime(const char *buf, const char *format, struct tm *tm);
buf
A pointer to a buffer that contains the string to convert.
format
The format that you want to use for the time; see "Formats," below.
%a
Abbreviated weekday name (Example: Sun)
%A
Full weekday name (Example: Sunday)
%b
Abbreviated month name (Example: Mar)
%B
Full month name (Example: March)
%c
Date and time representation (Example: Sun Aug 19 02:56:02 2012)
%d
Day of the month (01-31) (Example: 19)
%H
Hour in 24h format (00-23) (Example: 14)
%I
Hour in 12h format (01-12) (Example: 05)
%j
Day of the year (001-366) (Example: 231)
%m
Month as a decimal number (01-12) (Example: 08)
%M
Minute (00-59) (Example: 55)
%p
AM or PM designation (Example: PM)
%S
Second (00-61) (Example: 02)
%U
Week number with the first Sunday as the first day of week one (00-53) (Example: 33)
%w
Weekday as a decimal number with Sunday as 0 (0-6) (Example: 4)
%W
Week number with the first Monday as the first day of week one (00-53) (Example: 34)
%x
Date representation (Example: 08/19/12)
%X
Time representation (Example: 02:50:06)
%y
Year, last two digits (00-99) (Example: 01)
%Y
Year (Example: 2012)
%Z
Timezone name or abbreviation (Example: CDT)
%%
A % sign (Example: %)
tm
A pointer to a tm structure where the function can store the time. Any whitespace (as specified by isspace()) encountered before a directive is scanned in either the format string or the input string will be ignored. A directive that is an ordinary character must exactly match the next scanned character in the input string. Case is relevant when matching ordinary character directives. If the ordinary character directive in the format string does not match the character in the input string, strptime() is not successful. No more characters will be scanned. Any other conversion specification is matched by scanning characters in the input string until a character that is not a possible character for that specification is found or until no more characters can be scanned. If the specification was string-to-number, the possible character range is +,- or a character specified by isdigit(). Number specifiers do not require leading zeros. If the specification needs to match a field in the current locale, scanning is repeated until a match is found. Case is ignored when matching fields in the locale. If a match is found, the structure pointed to by tm will be updated with the corresponding locale information. If no match is found, strptime() is not successful. No more characters will be scanned. Missing fields in the tm structure may be filled in by strptime() if given enough information. For example, if a date is given, tm_yday can be calculated. Each standard conversion specification is replaced by appropriate characters as described in the following table: Some conversion specifiers can be modified by the E or O modifier characters to indicate that an alternate format or specification should be used. If a modified conversion specifier uses a field in the current locale that is unavailable, then the behavior will be as if the unmodified conversion specification were used. For example, if the era string is the empty string "", which means that era is unavailable, then %EY would act like %Y.
%Ec
Date/time for current era.
%EC
Era name.
%Ex
Date for current era.
%EX
Time for current era.
%Ey
Era year. This is the offset from the base year.
%EY
Year for the current era.
%Od
Day of the month using alternate digits.
%Oe
Same as %Od.
%OH
Hour in 24-hour format using alternate digits.
%OI
Hour in 12-hour format using alternate digits.
%Om
Month using alternate digits.
%OM
Minutes using alternate digits.
%OS
Seconds using alternate digits.
%Ou
Day of the week using alternate digits. Monday is 1 and Sunday is 7.
%OU
Week number of the year using alternate digits. Sunday is the first day of the week.
%OV
ISO week number of the year using alternate digits. See %V for explanation of ISO week number.
%Ow
Weekday using alternate digit. Sunday is 0 and Saturday is 6.
%OW
Week number of the year using alternate digits. Monday is the first day of the week.
%Oy
2-digit year using alternate digits.
%OZ
Abbreviated time zone name.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46
/* convert string to date/time by strptime() time function code example */ #include <stdio.h> #include <locale.h> #include <time.h> int main(void) { char buf[100]; time_t t; struct tm *timeptr,result; setlocale(LC_ALL,"/QSYS.LIB/EN_US.LOCALE"); t = time(NULL); timeptr = localtime(&t); strftime(buf,sizeof(buf), "%a %m/%d/%Y %r", timeptr); if (strptime(buf, "%a %m/%d/%Y %r",&result) == NULL) printf("\nstrptime failed\n"); else { printf("tm_hour: %d\n",result.tm_hour); printf("tm_min: %d\n",result.tm_min); printf("tm_sec: %d\n",result.tm_sec); printf("tm_mon: %d\n",result.tm_mon); printf("tm_mday: %d\n",result.tm_mday); printf("tm_year: %d\n",result.tm_year); printf("tm_yday: %d\n",result.tm_yday); printf("tm_wday: %d\n",result.tm_wday); } return 0; } /************************************************************ The output should be similar to: Tue 10/30/2001 10:59:10 AM tm_hour: 10 tm_min: 59 tm_sec: 10 tm_mon: 9 tm_mday: 30 tm_year: 101 tm_yday: 302 tm_wday: 2 ************************************************************/


Program to Fibonacci Series. Fibonacci Series generates subsequent number by adding two previous numbers and Fibonacci Series starts from 2 numbers F0 & F1. The initial values of
Take the height of a person as input and store it in the variable height. If the variable height is lesser than 150 cm, then print the output as "Dwarf". If the variable height is lesser than...
In this article we have shared two C programs to check if the input number is palindrome or not. 1) using while loop 2) using recursion. If a number 'remains same', even if we reverse its
Enter the number of queens(say n) and watch how computer places them in (n x n) matrix such that none can meet another moving along horizontally, vertically or digonally.