🚀⚡Beginner

Add Two Numbers

Add two integers entered by user

This program takes two integers as input from the user and displays their sum. It's a fundamental program that teaches variable declaration, user input, arithmetic operations, and formatted output.

📚 What You'll Learn

•Declaring integer variables with int
•Reading integers using scanf() with %d
•Using the address-of operator &
•Performing arithmetic operations

C Program to Add Two Numbers

add_two_numbers.c

1#include <stdio.h>
2
3int main() {
4    // Declare variables to store numbers and result
5    int num1, num2, sum;
6    
7    // Get first number from user
8    printf("Enter first number: ");
9    scanf("%d", &num1);
10    
11    // Get second number from user
12    printf("Enter second number: ");
13    scanf("%d", &num2);
14    
15    // Calculate sum
16    sum = num1 + num2;
17    
18    // Display the result
19    printf("%d + %d = %d\n", num1, num2, sum);
20    
21    return 0;
22}

Output

Enter first number: 25

Enter second number: 17

25 + 17 = 42

Detailed Code Explanation

Line 4int num1, num2, sum;

Declares three integer variables. Memory is allocated for each variable.

Variable Declaration Syntax:

data_type variable_name;

Multiple variables of same type can be declared in one line, separated by commas.

Line 8scanf("%d", &num1);

Reads an integer from user and stores it in num1.

Part	Meaning
%d	Format specifier for integer (decimal)
&num1	Address of num1 (where to store the value)

⚠️ Important: The & (address-of) operator is required for scanf() with basic data types like int, float, char. It tells scanf WHERE to store the input.

Line 15sum = num1 + num2;

The + operator adds the values and = stores the result.

Arithmetic Operators in C:

+

Add

-

Subtract

*

Multiply

/

Divide

%

Modulus

Line 18printf("%d + %d = %d\n", num1, num2, sum);

Multiple format specifiers are replaced by corresponding arguments in order:
First %d → num1, Second %d → num2, Third %d → sum

Step-by-Step Execution:

Variables Declared

Memory allocated for num1, num2, and sum (each 4 bytes for int)

First Prompt

printf displays "Enter first number: "

First Input

User types 25, scanf stores it at address of num1

Second Prompt

printf displays "Enter second number: "

Second Input

User types 17, scanf stores it at address of num2

Calculation

sum = 25 + 17 = 42

Display Result

printf shows "25 + 17 = 42"

Memory Visualization

num1

0x1000

num2

0x1004

sum

0x1008

Alternative Methods

Without Using Third Variable

main.c

1printf("Sum = %d\n", num1 + num2);  // Direct calculation in printf

Reading Both Numbers at Once

main.c

1printf("Enter two numbers: ");
2scanf("%d %d", &num1, &num2);  // Space-separated input

⚠️ Common Mistakes to Avoid

• Forgetting &: scanf("%d", num1) ❌ crashes! Use scanf("%d", &num1) ✓
• Wrong format specifier: Using %f for integers
• Integer overflow: Adding very large numbers exceeds int range

📝 Key Takeaways

✓int stores whole numbers

✓%d format specifier for integers

✓& is required in scanf for variables

✓+ operator adds two numbers

Print an Integer Entered By User

Check Whether a Number is Prime

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Print an Integer Entered By User

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Check Whether a Number is Prime

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