C Functions

What Is a Function?

In general terms, a function is also called a subroutine in some other languages like php, python and so on. Function is a self contained block of code that performs a specific task. A programmer define a function using its predefined syntax, a programmer can then call that function from elsewhere in your program.

Why Function?

• They avoid duplicating codes.
• They make it easier to eliminate errors.
• Function help you break down a big project.

Function and Arguments

A function often accepts none, one or more arguments, which are values passed to the function by the code that calls it. The function is capable of read and work on those arguments. A function may also optionally return a value(non void type) that can then be read by the calling code. in this way, the calling code will communicate with the function.

How Program thinks?

Program think of a function as a black box. The code that calls a function doesn't need to know what's inside the function, it just uses the function to get the job done.

Syntax

return-type function-name (arguments); 
main()
{
.
.
statements within main function; 
printf("%d", function-name (arguments));    //function call
.
}
return-type function-name (arguments)      //function definition
{
.
.
statements within user-defined function;
.
return variablename;
}

Types Of Function

There are two types of functions they are,

• Library Functions
• User Defined functions

Library Functions

C provides many pre-defined functions to perform a task, those functions are defined in an appropriate header files.

• printf()
• scanf()
• strlen()
• sqrt() and so on

User Defined Functions

C allows users or programmers to define a function according to their requirement. The main() function is also a user-defined function because the statements inside the main function is defined by the user, only the function name is defined in a library.

Function Declaration

• The function declaration statement informs the compiler about a function return type, function name and parameters or arguments type.
• Syntax : return-type function-name (arguments);
• Return type : return type is the data type of the value which is given back to the calling function.
• function name : function name is the name of a function. A function is called by using the function name. The naming rules are same as variable naming.
• parameters or arguments type : C allows programmers to pass information to the called function from the calling function by using parameters. These parameters are variables of data type.

C program - Functions

The following example program will clearly explain the concept of functions

#include <stdio.h>
int main()
{
//main function definition
int a = 5, b = 10;
int sum;
printf("The value of a and b : %d %d ", a, b);
sum = add(a, b);    //function call
printf("\nsum = %d ", sum);
}
//function definition
int add(int a, int b)
{
int c;
c = a + b;
return c;    //returns a integer value to the calling function
}

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