In C language, a program to add two numbers involves taking two numbers as input from the user, performing the addition, and then printing the result. Here's a step-by-step explanation and a sample code for the program:

Steps for Addition of Two Numbers:

1. Include Header Files: You need to include the stdio.h library, which is required for input and output functions like printf and scanf.
2. Declare Variables: Define variables that will store the numbers to be added and the result of their sum.
3. Take Input: Use the scanf function to take input from the user for the two numbers.
4. Perform Addition: Add the two numbers and store the result in another variable.
5. Display Output: Use printf to display the sum of the numbers.

Program:

#include <stdio.h>

int main() {
    int num1, num2, sum; // Declare variables for two numbers and the result
    
    // Ask the user to enter the two numbers
    printf("Enter two integers: ");
    
    // Read the input from the user and store them in num1 and num2
    scanf("%d %d", &num1, &num2);
    
    // Add the two numbers
    sum = num1 + num2;
    
    // Display the result of the addition
    printf("Sum of %d and %d is: %d\n", num1, num2, sum);
    
    return 0;
}

Explanation:

1. #include <stdio.h>: This includes the Standard Input Output library, which contains functions like printf (for output) and scanf (for input).

2. Variables:

   • int num1, num2, sum: Three variables are declared of type int. num1 and num2 will store the numbers entered by the user, and sum will store the result of their addition.

3. Input:

   • printf("Enter two integers: "); prompts the user to enter two numbers.
   • scanf("%d %d", &num1, &num2); reads two integers entered by the user and stores them in the variables num1 and num2.

4. Addition:

   • sum = num1 + num2; calculates the sum of the two numbers.

5. Output:

   • printf("Sum of %d and %d is: %d\n", num1, num2, sum); prints the result, showing the sum of the two numbers.

Sample Output:

Enter two integers: 12 25
Sum of 12 and 25 is: 37

Key Points:

• %d is used as a format specifier for integers.
• scanf uses & to pass the address of variables where the input values will be stored.
• The program adds the two integers entered by the user and prints their sum.

This is a simple and effective program to get started with user input, variable handling, and performing basic arithmetic operations in C.