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C Programming Code Examples

C > Sorting Searching Code Examples

Qsort [string array]

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/* Qsort [string array] */ #include <stdio.h> #include <string.h> #include <stdlib.h> void sortstrarr(void *array, unsigned n); static int cmpr(const void *a, const void *b); int main(void) { char line[1024]; char *line_array[1024]; int i = 0; int j = 0; while((fgets(line, 1024, stdin)) != NULL) if(i < 1024) line_array[i++] = strdup(line); else break; sortstrarr(line_array, i); while(j < i) printf("%s", line_array[j++]); return 0; } static int cmpr(const void *a, const void *b) { return strcmp(*(char **)a, *(char **)b); } void sortstrarr(void *array, unsigned n) { qsort(array, n, sizeof(char *), cmpr); }
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.
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/* 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; }
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).
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/* 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; }
sizeof() Operator in C
The sizeof() operator is commonly used in C. It determines the size of the expression or the data type specified in the number of char-sized storage units. The sizeof() operator contains a single operand which can be either an expression or a data typecast where the cast is data type enclosed within parenthesis. The data type cannot only be primitive data types such as integer or floating data types, but it can also be pointer data types and compound data types such as unions and structs.
Syntax for sizeof() Operator in C
#include <stdio.h> sizeof (data type)
data type
Where data type is the desired data type including classes, structures, unions and any other user defined data type. Mainly, programs know the storage size of the primitive data types. Though the storage size of the data type is constant, it varies when implemented in different platforms. For example, we dynamically allocate the array space by using sizeof() operator:
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/* return the size of a variable by sizeof() operator example */ int main( int argc, char* argv[] ) { printf("sizeof(char) = %d\n", sizeof(char) ); printf("sizeof(short) = %d\n", sizeof(short) ); printf("sizeof(int) = %d\n", sizeof(int) ); printf("sizeof(long) = %d\n", sizeof(long) ); printf("sizeof(long long) = %d\n", sizeof(long long) ); printf("\n"); printf("sizeof(unsigned char) = %d\n", sizeof(unsigned char) ); printf("sizeof(unsigned short) = %d\n", sizeof(unsigned short) ); printf("sizeof(unsigned int) = %d\n", sizeof(unsigned int) ); printf("sizeof(unsigned long) = %d\n", sizeof(unsigned long) ); printf("\n"); printf("sizeof(float) = %d\n", sizeof(float) ); printf("sizeof(double) = %d\n", sizeof(double) ); printf("sizeof(long double) = %d\n", sizeof(long double) ); printf("\n"); int x; printf("sizeof(x) = %d\n", sizeof(x) ); }
Relational Operators in C
Relational Operators are the operators used to create a relationship and compare the values of two operands. For example, there are two numbers, 5 and 15, and we can get the greatest number using the greater than operator (>) that returns 15 as the greatest or larger number to the 5. Following are the various types of relational operators in C.
==
Equal To Operator (==) is used to compare both operands and returns 1 if both are equal or the same, and 0 represents the operands that are not equal.
!=
Not Equal To Operator (!=) is the opposite of the Equal To Operator and is represented as the (!=) operator. The Not Equal To Operator compares two operands and returns 1 if both operands are not the same; otherwise, it returns 0.
<
Less than Operator (<) is used to check whether the value of the left operand is less than the right operand, and if the statement is true, the operator is known as the Less than Operator.
>
Greater than Operator (>) checks the value of the left operand is greater than the right operand, and if the statement is true, the operator is said to be the Greater Than Operator.
<=
Less than Equal To Operator (<=) checks whether the value of the left operand is less than or equal to the right operand, and if the statement is true, the operator is said to be the Less than Equal To Operator.
>=
Greater than Equal To Operator (>=) checks whether the left operand's value is greater than or equal to the right operand. If the statement is true, the operator is said to be the Greater than Equal to Operator.
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/* relational operators in C */ #include <stdio.h> main() { int a = 23; int b = 9; int c ; if( a == b ) { printf("Line 1 - a is equal to b\n" ); } else { printf("Line 1 - a is not equal to b\n" ); } if ( a < b ) { printf("Line 2 - a is less than b\n" ); } else { printf("Line 2 - a is not less than b\n" ); } if ( a > b ) { printf("Line 3 - a is greater than b\n" ); } else { printf("Line 3 - a is not greater than b\n" ); } /* Lets change value of a and b */ a = 5; b = 20; if ( a <= b ) { printf("Line 4 - a is either less than or equal to b\n" ); } if ( b >= a ) { printf("Line 5 - b is either greater than or equal to b\n" ); } }
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.
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/* 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; }
strcmp() Function in C
Compare two strings. Compares the C string str1 to the C string str2. This function starts comparing the first character of each string. If they are equal to each other, it continues with the following pairs until the characters differ or until a terminating null-character is reached. This function performs a binary comparison of the characters. For a function that takes into account locale-specific rules, see strcoll.
Syntax for strcmp() Function in C
#include <string.h> int strcmp ( const char * str1, const char * str2 );
str1
C string to be compared.
str2
C string to be compared. Function returns an integral value indicating the relationship between the strings: • <0 the first character that does not match has a lower value in ptr1 than in ptr2 • 0 the contents of both strings are equal • >0 the first character that does not match has a greater value in ptr1 than in ptr2 The strcmp() function is used to compare two strings two strings str1 and str2. If two strings are same then strcmp() returns 0, otherwise, it returns a non-zero value. This function compares strings character by character using ASCII value of the characters. The comparison stops when either end of the string is reached or corresponding characters are not same. The non-zero value returned on mismatch is the difference of the ASCII values of the non-matching characters of two strings.
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/* compare two strings and return an integer value based on the result by strcmp() function example. */ #include <stdio.h> #include <string.h> int main () { char str1[15]; char str2[15]; int ret; strcpy(str1, "abcdef"); strcpy(str2, "ABCDEF"); ret = strcmp(str1, str2); if(ret < 0) { printf("str1 is less than str2"); } else if(ret > 0) { printf("str2 is less than str1"); } else { printf("str1 is equal to str2"); } return(0); }
What is an Array in C Language
An array is defined as the collection of similar type of data items stored at contiguous memory locations. Arrays are the derived data type in C programming language which can store the primitive type of data such as int, char, double, float, etc. It also has the capability to store the collection of derived data types, such as pointers, structure, etc. The array is the simplest data structure where each data element can be randomly accessed by using its index number. C array is beneficial if you have to store similar elements. For example, if we want to store the marks of a student in 6 subjects, then we don't need to define different variables for the marks in the different subject. Instead of that, we can define an array which can store the marks in each subject at the contiguous memory locations. By using the array, we can access the elements easily. Only a few lines of code are required to access the elements of the array.
Properties of Array
The array contains the following properties. • Each element of an array is of same data type and carries the same size, i.e., int = 4 bytes. • Elements of the array are stored at contiguous memory locations where the first element is stored at the smallest memory location. • Elements of the array can be randomly accessed since we can calculate the address of each element of the array with the given base address and the size of the data element.
Advantage of C Array
• 1) Code Optimization: Less code to the access the data. • 2) Ease of traversing: By using the for loop, we can retrieve the elements of an array easily. • 3) Ease of sorting: To sort the elements of the array, we need a few lines of code only. • 4) Random Access: We can access any element randomly using the array.
Disadvantage of C Array
• 1) Allows a fixed number of elements to be entered which is decided at the time of declaration. Unlike a linked list, an array in C is not dynamic. • 2) Insertion and deletion of elements can be costly since the elements are needed to be managed in accordance with the new memory allocation.
Declaration of C Array
To declare an array in C, a programmer specifies the type of the elements and the number of elements required by an array as follows
type arrayName [ arraySize ];
This is called a single-dimensional array. The arraySize must be an integer constant greater than zero and type can be any valid C data type. For example, to declare a 10-element array called balance of type double, use this statement
double balance[10];
Here balance is a variable array which is sufficient to hold up to 10 double numbers.
Initializing Arrays
You can initialize an array in C either one by one or using a single statement as follows
double balance[5] = {850, 3.0, 7.4, 7.0, 88};
The number of values between braces { } cannot be larger than the number of elements that we declare for the array between square brackets [ ]. If you omit the size of the array, an array just big enough to hold the initialization is created. Therefore, if you write
double balance[] = {850, 3.0, 7.4, 7.0, 88};
Accessing Array Elements
An element is accessed by indexing the array name. This is done by placing the index of the element within square brackets after the name of the array.
double salary = balance[9];
The above statement will take the 10th element from the array and assign the value to salary variable.
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/* arrays in C Language */ #include<stdio.h> void main () { int i, j,temp; int a[10] = { 4, 8, 16, 120, 36, 44, 13, 88, 90, 23}; for(i = 0; i<10; i++) { for(j = i+1; j<10; j++) { if(a[j] > a[i]) { temp = a[i]; a[i] = a[j]; a[j] = temp; } } } printf("Printing Sorted Element List ...\n"); for(i = 0; i<10; i++) { printf("%d\n",a[i]); } }
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.
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/* 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; }
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.
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/* 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; }
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.
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/* 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; }
gets() Function in C
Get string from stdin. Reads characters from the standard input (stdin) and stores them as a C string into str until a newline character or the end-of-file is reached. The newline character, if found, is not copied into str. A terminating null character is automatically appended after the characters copied to str. Notice that gets is quite different from fgets: not only gets uses stdin as source, but it does not include the ending newline character in the resulting string and does not allow to specify a maximum size for str (which can lead to buffer overflows). The gets() function enables the user to enter some characters followed by the enter key. All the characters entered by the user get stored in a character array. The null character is added to the array to make it a string. The gets() allows the user to enter the space-separated strings. It returns the string entered by the user.
Syntax for gets() Function in C
#include<stdio.h> char * gets ( char * str );
str
Pointer to a block of memory (array of char) where the string read is copied as a C string. On success, the function returns str. If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged). If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).
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/* read characters from the standard input (stdin) and stores them as a C string */ #include<stdio.h> #include<conio.h> #include<stdlib.h> void main() { clrscr(); FILE *fp; char fname[20]; printf("Enter filename : "); gets(fname); fp=fopen(fname, "r"); if(fp==NULL) { printf("Error in opening the file..!!\n"); printf("Press any key to exit..\n"); getch(); exit(1); } fclose(fp); getch(); }
qsort() Function in C
Sort elements of array. Sorts the num elements of the array pointed to by base, each element size bytes long, using the compar function to determine the order. The sorting algorithm used by this function compares pairs of elements by calling the specified compar function with pointers to them as argument. The function does not return any value, but modifies the content of the array pointed to by base reordering its elements as defined by compar. The order of equivalent elements is undefined.
Syntax for qsort() Function in C
#include <stdlib.h> void qsort (void* base, size_t num, size_t size, int (*compar)(const void*,const void*));
base
Pointer to the first object of the array to be sorted, converted to a void*.
num
Number of elements in the array pointed to by base. size_t is an unsigned integral type.
size
Size in bytes of each element in the array. size_t is an unsigned integral type.
compar
Pointer to a function that compares two elements. This function is called repeatedly by qsort to compare two elements. It shall follow the following prototype:
int compar (const void* p1, const void* p2);
Taking two pointers as arguments (both converted to const void*). The function defines the order of the elements by returning (in a stable and transitive manner): • <0 The element pointed to by p1 goes before the element pointed to by p2 • 0 The element pointed to by p1 is equivalent to the element pointed to by p2 • > 0 The element pointed to by p1 goes after the element pointed to by p2 Sorts an array using the quick-sort algorithm. The qsort() function sorts the array referenced by its first argument according to a user-definable sorting criterion using the quick-sort algorithm. You determine the sorting criterion by defining a callback function that compares two array elements in some way and indicates which is greater. The qsort() function calls this function by the pointer passed in the last argument to qsort() each time it needs to compare two elements of the array. The comparison function takes as its arguments two pointers to elements of the array being sorted. The corresponding parameters are declared as void pointers, so that qsort() can be used with any type of array element. The comparison must return a negative value if its first argument is "less than" the second, a positive value if the first argument is "greater than" the second, or zero if they are "equal." It is up to you to define the criteria that constitute these relations for the given type of array element. The qsort() function sorts the array in ascending order. The same comparison function can be used by the bsearch() function. This function does not return any value.
Complexity
Unspecified, but quicksorts are generally linearithmic in num, on average, calling compar approximately num*log2(num) times.
Data races
The function accesses and/or modifies the num elements in the array pointed to by base.
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/* sort elements of array by qsort() function code example */ #include <stdio.h> #include <stdlib.h> int values[] = { 44, 39, 13, 82, 23 }; int cmpfunc (const void * a, const void * b) { return ( *(int*)a - *(int*)b ); } int main () { int n; printf("Before sorting the list is: \n"); for( n = 0 ; n < 5; n++ ) { printf("%d ", values[n]); } qsort(values, 5, sizeof(int), cmpfunc); printf("\nAfter sorting the list is: \n"); for( n = 0 ; n < 5; n++ ) { printf("%d ", values[n]); } return(0); }
fgets() Function in C
Get string from stream. Reads characters from stream and stores them as a C string into str until (num-1) characters have been read or either a newline or the end-of-file is reached, whichever happens first. A newline character makes fgets stop reading, but it is considered a valid character by the function and included in the string copied to str. A terminating null character is automatically appended after the characters copied to str. Notice that fgets is quite different from gets: not only fgets accepts a stream argument, but also allows to specify the maximum size of str and includes in the string any ending newline character.
Syntax for fgets() Function in C
#include <stdio.h> char * fgets ( char * str, int num, FILE * stream );
str
Pointer to an array of chars where the string read is copied.
num
Maximum number of characters to be copied into str (including the terminating null-character).
stream
Pointer to a FILE object that identifies an input stream. stdin can be used as argument to read from the standard input. On success, the function returns str. If the end-of-file is encountered while attempting to read a character, the eof indicator is set (feof). If this happens before any characters could be read, the pointer returned is a null pointer (and the contents of str remain unchanged). If a read error occurs, the error indicator (ferror) is set and a null pointer is also returned (but the contents pointed by str may have changed).
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/* get string from stream by fgets() function example */ #include<stdio.h> #include<stdlib.h> int main() { char str[50]; FILE *fp; fp = fopen("myfile2.txt", "r"); if(fp == NULL) { printf("Error opening file\n"); exit(1); } printf("Testing fgets() function: \n\n"); printf("Reading contents of myfile.txt: \n\n"); while( fgets(str, 30, fp) != NULL ) { puts(str); } fclose(fp); return 0; }
#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.
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/* #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; }


C code implements Pancake Sort on array of integers. Pancake sorting is a variation of the "Sorting Problem" in which the only allowed operation is to reverse the elements of some
Accepts the sentence and replaces lowercase characters by uppercase and vice-versa. Take an an English sentence as input and store it in the array "sentence[]". Copy the Last Letter's
C Program take a octal number as input and store it in the array octalnumber and using switch statement access each digit of a octal number and print its equivalent binary value