Reverse a Number in C++

This program teaches you how to reverse a number in C++. Reversing a number means reading its digits from right to left instead of left to right. For example, reversing 1234 gives 4321. This is a common programming problem that helps you understand digit manipulation, loops, and number operations.

What This Program Does

The program takes a number and reverses its digits. For example:

Input: 1234
Output: 4321

The process involves extracting digits from the right (one's place, ten's place, etc.) and building a new number from left to right.

Algorithm

The core logic uses a while loop:

cpp
while (num != 0) {
    remainder = num % 10;
    reversed = reversed * 10 + remainder;
    num /= 10;
}

Step-by-step for num = 1234:

Extract last digit: 1234 % 10 = 4, reversed = 4
Remove last digit: 1234 / 10 = 123
Extract last digit: 123 % 10 = 3, reversed = 43
Remove last digit: 123 / 10 = 12
Continue until num becomes 0
Final result: reversed = 4321

Key Operations

Modulo Operator (%):

num % 10 gives the last digit of the number
Example: 1234 % 10 = 4, 123 % 10 = 3

Integer Division (/):

num / 10 removes the last digit
Example: 1234 / 10 = 123, 123 / 10 = 12

Building the Reversed Number:

reversed = reversed * 10 + remainder
This shifts existing digits left and adds the new digit on the right
Example: If reversed = 43 and remainder = 2, then 43 * 10 + 2 = 432

Edge Cases

Zero: 0 reversed is still 0
Single Digit: 5 reversed is 5
Numbers Ending in Zero: 100 reversed = 1 (leading zeros are dropped)
Negative Numbers: This program doesn't handle negatives (convert absolute value first)

Summary

Reversing a number extracts digits from right to left using modulo and division.
The reversed number is built by shifting digits left and adding new digits on the right.
Modulo (%) extracts the last digit, division (/) removes the last digit.
This algorithm is fundamental for understanding digit manipulation and number operations.

This program is essential for learning digit manipulation, understanding loops, and solving number-related problems in C++.

Output