FAQs in C: Program to Swap Two Numbers

Let’s go through both methods for swapping two numbers: using a temporary variable and without using a temporary variable.

Method 1: Swapping Two Numbers Using a Temporary Variable

Step 1: Start
Step 2: Input: Read two integers a and b from the user.
Step 3: Process:
        Declare a temporary variable temp.
        Assign the value of a to temp.
        Assign the value of b to a.
        Assign the value of temp to b.
Step 4: Output: Display the values of a and b after swapping.
Step 5: End

C Program (Using a Temporary Variable)

#include <stdio.h>

int main() {
    int a, b, temp;

    // Step 2: Read two integers from the user
    printf("Enter two integers (a and b): ");
    scanf("%d %d", &a, &b);

    // Step 3: Swap the values using a temporary variable
    temp = a;  // Store the value of a in temp
    a = b;     // Assign the value of b to a
    b = temp;  // Assign the value of temp to b

    // Step 4: Output the swapped values
    printf("After swapping: a = %d, b = %d\n", a, b);

    // Step 5: End
    return 0;
}

Explanation of Each Step

Include Header: This line includes the standard input-output library.

Main Function: The main function is the entry point of the C program.

Variable Declaration: Three integer variables a, b, and temp are declared. a and b will store the user inputs, and temp will be used for swapping.

Reading Input:

• printf prompts the user to enter two integers.

• scanf reads the integers and stores them in variables a and b.

Swapping Using a Temporary Variable:

• The value of a is stored in temp.
• The value of b is assigned to a.
• This value is stored in temp (initial value of a) is assigned to b.

Output: This line prints the swapped values of a and b.

End: This line indicates successful completion of the program.

Method 2: Swapping Two Numbers Without Using a Temporary Variable

Step 1: Start
Step 2: Input: Read two integers a and b from the user.
Step 3: Process:
        Use arithmetic operations to swap the values.
        a = a + b
        b = a - b
        a = a - b
Step 5: Output: Display the values of a and b after swapping.
Step 6: End

C Program (Without Using a Temporary Variable)

#include <stdio.h>

int main() {
    int a, b;

    // Step 2: Read two integers from the user
    printf("Enter two integers (a and b): ");
    scanf("%d %d", &a, &b);

    // Step 3: Swap the values without using a temporary variable
    a = a + b;  // a now holds the sum of a and b
    b = a - b;  // b now holds the original value of a
    a = a - b;  // a now holds the original value of b

    // Step 4: Output the swapped values
    printf("After swapping: a = %d, b = %d\n", a, b);

    // Step 5: End
    return 0;
}

Explanation of each step:

Include Header: This line includes the standard input-output library.

Main Function: The main function is the entry point of the C program.

Variable Declaration: Two integer variables a and b are declared to store the user inputs.

Reading Input:

• printf prompts the user to enter two integers.

• scanf reads the integers and stores them in variables a and b.

Swapping Without Using a Temporary Variable:

• a = a + b stores the sum of a and b in a.
• b = a – b assigns the original value of a to b (since a now holds a + b, a – b results in the original a).
• a = a – b assigns the original value of b to a (since b now holds the original a).

Output: This line prints the swapped values of a and b.

End: This line indicates successful completion of the program.