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C Programming Code Examples

C > Functions Code Examples

Demonstraction of function call

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/* Demonstraction of function call */ void function2(void){ printf ("2 \n"); } void function1 (void) { printf ("1 \n"); printf ("1 \n"); function2 ( ); printf ("1 \n"); printf ("1 \n"); } int main ( ) { printf ("\n"); printf ("c.happycodings.com\n"); printf ("C Programming Language\n"); printf ("\n"); printf ("\n"); function1(); printf ("\n"); printf ("c.happycodings.com\n"); printf ("C Programming Language\n"); printf ("\n"); return 0; }
Standard Input/Output Devices in C
When we say Input, it means to feed some data into a program. An input can be given in the form of a file or from the command line. C programming provides a set of built-in functions to read the given input and feed it to the program as per requirement. When we say Output, it means to display some data on screen, printer, or in any file. C programming provides a set of built-in functions to output the data on the computer screen as well as to save it in text or binary files. C programming treats all the devices as files. So devices such as the display are addressed in the same way as files and the following three files are automatically opened when a program executes to provide access to the keyboard and screen. • Standard input: stdin(Keyboard). • Standard output: stdout(Screen). • Standard error: stderr(Your screen). The file pointers are the means to access the file for reading and writing purpose. This section explains how to read values from the screen and how to print the result on the screen.
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/* C language provides standard library functions to read any given input and to display data on the console. */ #include<stdlib.h> #include<stdio.h> int main() { char chr; float num1; double num2; int i; printf("Enter a character: "); scanf("%c", &chr); // When %c is used, a character is displayed printf("You entered %c.\n",chr); // When %d is used, ASCII value is displayed printf("ASCII value is %d.", chr); printf("Enter a number: "); scanf("%f", &num1); printf("Enter another number: "); scanf("%lf", &num2); printf("num1 = %f\n", num1); printf("num2 = %lf", num2); printf("Enter a value: "); i = getchar(); printf("You entered: "); putchar(i); return 0; }
Return Statement in C
The return statement terminates the execution of a function and returns control to the calling function. Execution resumes in the calling function at the point immediately following the call. A return statement can also return a value to the calling function. A return statement causes your function to exit and hand back a value to its caller. The point of functions, in general, is to take in inputs and return something. The return statement is used when a function is ready to return a value to its caller.
Syntax for Return Statement in C
return[expression];
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/* end the processing of the current function and returns control to the caller of the function by return statement */ /* C program to find maximum between two numbers using function */ #include <stdio.h> /* Function declaration */ int max(int num1, int num2); int main() { int num1, num2, maximum; printf("Enter two numbers: "); scanf("%d%d", &num1, &num2); /* * Call max function with arguments num1 and num2 * Store the maximum returned to variable maximum */ maximum = max(num1, num2); printf("Maximum = %d", maximum); return 0; } /* Function definition */ int max(int num1, int num2) { int maximum; // Find maximum between two numbers if(num1 > num2) maximum = num1; else maximum = num2; // Return the maximum value to caller return maximum; }
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; }
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; }
Functions in C Language
A function is a group of statements that together perform a task. Every C program has at least one function, which is main(), and all the most trivial programs can define additional functions. You can divide up your code into separate functions. How you divide up your code among different functions is up to you, but logically the division is such that each function performs a specific task. A function declaration tells the compiler about a function's name, return type, and parameters. A function definition provides the actual body of the function. The C standard library provides numerous built-in functions that your program can call. For example, strcat() to concatenate two strings, memcpy() to copy one memory location to another location, and many more functions. A function can also be referred as a method or a sub-routine or a procedure, etc.
Defining a Function
The general form of a function definition in C programming language is as follows:
return_type function_name( parameter list ) { body of the function }
A function definition in C programming consists of a function header and a function body. Here are all the parts of a function:
Return Type
A function may return a value. The return_type is the data type of the value the function returns. Some functions perform the desired operations without returning a value. In this case, the return_type is the keyword void.
Function Name
This is the actual name of the function. The function name and the parameter list together constitute the function signature.
Parameters
A parameter is like a placeholder. When a function is invoked, you pass a value to the parameter. This value is referred to as actual parameter or argument. The parameter list refers to the type, order, and number of the parameters of a function. Parameters are optional; that is, a function may contain no parameters.
Function Body
The function body contains a collection of statements that define what the function does. Given below is the source code for a function called max(). This function takes two parameters num1 and num2 and returns the maximum value between the two:
/* function returning the max between two numbers */ int max(int num1, int num2) { /* local variable declaration */ int result; if (num1 > num2) result = num1; else result = num2; return result; }
Function Declarations
A function declaration tells the compiler about a function name and how to call the function. The actual body of the function can be defined separately. A function declaration has the following parts:
return_type function_name( parameter list );
For the above defined function max(), the function declaration is as follows:
int max(int num1, int num2);
Parameter names are not important in function declaration only their type is required, so the following is also a valid declaration:
int max(int, int);
Function declaration is required when you define a function in one source file and you call that function in another file. In such case, you should declare the function at the top of the file calling the function.
Calling a Function
While creating a C function, you give a definition of what the function has to do. To use a function, you will have to call that function to perform the defined task. When a program calls a function, the program control is transferred to the called function. A called function performs a defined task and when its return statement is executed or when its function-ending closing brace is reached, it returns the program control back to the main program. To call a function, you simply need to pass the required parameters along with the function name, and if the function returns a value, then you can store the returned value.
Function Arguments
If a function is to use arguments, it must declare variables that accept the values of the arguments. These variables are called the formal parameters of the function. Formal parameters behave like other local variables inside the function and are created upon entry into the function and destroyed upon exit. While calling a function, there are two ways in which arguments can be passed to a function: Call by value: This method copies the actual value of an argument into the formal parameter of the function. In this case, changes made to the parameter inside the function have no effect on the argument. Call by reference: This method copies the address of an argument into the formal parameter. Inside the function, the address is used to access the actual argument used in the call. This means that changes made to the parameter affect the argument. There are the following advantages of C functions. • By using functions, we can avoid rewriting same logic/code again and again in a program. • We can call C functions any number of times in a program and from any place in a program. • We can track a large C program easily when it is divided into multiple functions. • Reusability is the main achievement of C functions. • However, Function calling is always a overhead in a C program.
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/* creating a user defined function addition() */ #include <stdio.h> int addition(int num1, int num2) { int sum; /* Arguments are used here*/ sum = num1+num2; /* Function return type is integer so we are returning * an integer value, the sum of the passed numbers. */ return sum; } int main() { int var1, var2; printf("Enter number 1: "); scanf("%d",&var1); printf("Enter number 2: "); scanf("%d",&var2); /* Calling the function here, the function return type * is integer so we need an integer variable to hold the * returned value of this function. */ int res = addition(var1, var2); printf ("Output: %d", res); return 0; }


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