A function is a module or block of program code which deals with a particular task.

function will make code
reusable
it stop be mixing on coding
It avoid repeating parts of the programming coding

let make our add_integer to function and run it.

here is modified code, Blue color text show the changes we did to our previous code.

#include<stdio.h> // standard input output header file
#include<conio.h>
main()
{
int a,b;

printf("enter any number");
scanf("%d",&a); // or cin >> a
printf("enter any number");
scanf("%d",&b);
Add_Two_Integers(a,b);
Add_Two_Integers(12,23);
getch();

}

Add_Two_Integers(a,b)               /* Add a and b */

int a,b;

{ int c;

c = a + b;
printf ("\n%d",c);

}

here it is in running