# 1. Introduction

One of the most fundamental operations in any programming language is arithmetic. Today, we'll create a simple C program that adds two numbers. While it sounds elementary, this exercise will familiarize beginners with important concepts like variable declaration, taking user input, and displaying output.

# 2. Program Overview

Our program will do the following:

1. Prompt the user to enter two numbers.

2. Read and store these numbers.

4. Display the sum.

# 3. Code Program

``````#include <stdio.h>  // Including the Standard I/O library for input and output functions

int main() {  // Entry point of the program

double num1, num2, sum;  // Declare three variables of type double for storing two numbers and their sum

// Prompting the user for input
printf("Enter first number: ");
scanf("%lf", &num1);  // Read and store the first number

printf("Enter second number: ");
scanf("%lf", &num2);  // Read and store the second number

sum = num1 + num2;  // Compute the sum of the two numbers

printf("The sum of %.2lf and %.2lf is: %.2lf\n", num1, num2, sum);  // Display the sum

return 0;  // Indicate successful termination
}
``````

### Output:

```If the user enters 5 and 6.5:
Enter first number: 5
Enter second number: 6.5
The sum of 5.00 and 6.50 is: 11.50
```

# 4. Step By Step Explanation

1. #include <stdio.h>: This includes the standard input/output library, which gives us access to functions like printf and scanf.

2. int main(): This is the starting point of our program. Every C program begins its execution from the main function.

3. double num1, num2, sum;: Here, we declare three variables of the double data type to store two numbers and their resulting sum.

4. printf function: Used for displaying prompts to the user. It sends formatted output to the screen.

5. scanf function: Allows us to read formatted input. We use %lf as the format specifier because we're dealing with double data types. The & symbol is used to get the address of the variable, i.e., where the inputted value will be stored in memory.

6. sum = num1 + num2;: This line performs the arithmetic addition operation.

7. return 0;: This returns an exit status. A return of 0 from the main indicates successful completion.

With this program, beginners get an introduction to user input, arithmetic operations, and displaying results in C programming.