The below program in C accepts 2 integer numbers and calculates the sum of those 2 numbers using add function.

add function accepts two integer parameters namely nos1 and nos2. This function then calculates the sum and return the result to the calling main function. Once the result is received, main function prints the addition of those two numbers

#include <stdio.h>
#include <stdlib.h>

int main(){

	int num1, num2, result;

	/*Accept the numbers from the user*/
	printf("\nEnter the two number: ");
	scanf("%d %d", &num1, &num2);

	/* Pass the value of num1 and num2 as parameter to function add.
	    The value returned is stored in the variable result
	 */
	result = add(num1, num2);
	printf("\nAddition of %d and %d is %d", num1, num2, result);

	return 1;
}

/*Defining the function add()*/
int add(int no1, int no2)
{
	int res;
	res = no1 + no2;
	return res;
}

Output:

Enter the two number: 5 96

Addition of 5 and 96 is 101