In C, a Reverse a Number program takes a number and reverses its digits. For example, if the input is 12345, the output will be 54321. This is typically done using a combination of mathematical operations like modulo (%) and division (/).

Logic to Reverse a Number:

1. Extract the last digit using the modulo operator (%).
2. Build the reverse number by appending the extracted digit.
3. Remove the last digit from the original number using division (/).
4. Repeat the process until all digits are reversed.

Program:

#include <stdio.h>

int main() {
    int num, reversed = 0, remainder;

    // Input a number from the user
    printf("Enter an integer: ");
    scanf("%d", &num);

    // While loop to reverse the digits of the number
    while (num != 0) {
        remainder = num % 10;           // Extract the last digit
        reversed = reversed * 10 + remainder;  // Build the reversed number
        num = num / 10;                 // Remove the last digit from the original number
    }

    // Output the reversed number
    printf("Reversed number = %d\n", reversed);

    return 0;
}

Explanation:

1. Variables:

   • int num: This stores the original number input by the user.
   • int reversed: This stores the reversed number, initialized to 0.
   • int remainder: This stores the remainder, which is the last digit of the original number.

2. Input:

   • scanf("%d", &num); takes the input number from the user.

3. Reversing Logic:

   • Extract the Last Digit: remainder = num % 10; extracts the last digit of num.
   • Build the Reverse Number: reversed = reversed * 10 + remainder; appends the extracted digit to reversed. Initially, reversed is 0, so for each digit, it multiplies by 10 and adds the new digit.
   • Remove the Last Digit: num = num / 10; removes the last digit from the original number by dividing it by 10.

4. Loop:

   • The process is repeated inside the while (num != 0) loop until the original number becomes 0, meaning all digits have been reversed.

5. Output:

   • The program prints the reversed number using printf.

Sample Output:

Example 1:

Enter an integer: 12345
Reversed number = 54321

Example 2:

Enter an integer: 67890
Reversed number = 9876

Key Points:

• Modulo Operation (%) is used to extract the last digit of the number.
• Division by 10 (/) is used to remove the last digit from the number.
• The reversed number is built by multiplying the current reversed value by 10 and adding the extracted digit.

This is a common beginner-level program in C, helping you understand loops, arithmetic operations, and basic input/output handling.