How to create a function in ‘C’

How can we make the function in ‘C’?

Main function

we can use main() for using function. main() mean start the program in C.

#include <stdio.h>
void main()
{
  printf ("Hello, World!");
}

Void

The Void means the function doesn’t have any return value. if you want to add a return. And after that, you can change the void to others.

Return something

for example, if you want to return int value…

int Sum (int value1, int value2)
{
  int result = value1 + value2;
  return result;
}

Using Caller

C is an assembly of functions. That means you can use various functions in a single program. The Caller is a function that calls other functions from outside of him.

#include <stdio.h>
int Sum (int value1, int value2) 
{
  return value1 + value2;
}
void main(void) 
{
  int a = 1;
  int b = 2;
  int c = Sum(a, b);
  printf("Sum of %d and %d is %d \n", a, b, c);
}

Function Prototype

C compute top to bottom. That means if you do not declare the function first, you will get an error.

/* error example */
void main(void) {
int a = 1;
int b = 2;
int c = Sum(a, b); /* ERROR! : can't find Sum() */
printf("Sum of %d and %d is %d \n", a, b, c);
}
int Sum (int value1, int value2) {
return value1 + value2;
}
return value1 + value2;
}

In this situation, you can use a function prototype, like below.

int Sum (int value1, int value2); 
/* without declare 'Sum' first, you'll get an error. */
void main(void) {
  int a = 1;
  int b = 2;
  int c = Sum(a, b);
  printf("Sum of %d and %d is %d \n", a, b, c);
}
int Sum (int value1, int value2) {
  return value1 + value2;
}