C++ Exercises: Reverse the digits of a given integer

Last update on April 12 2025 12:59:15 (UTC/GMT +8 hours)

3. Reverse Digits of an Integer

Write a C++ program to reverse the digits of a given integer.

Sample Input: 4
Sample Output: 4

Sample Input: 123
Sample Output: 321

Sample Solution:

C++ Code :

#include <iostream> // Include input/output stream library
using namespace std; // Using standard namespace

// Function to reverse an integer
int reverse_int(int x) {
    int res = 0; // Initialize the result variable to store the reversed integer

    // Loop to reverse the integer
    while (x != 0) {
        int pop = x % 10; // Extract the last digit of the number
        x = x / 10; // Update the number by removing its last digit

        int candidate = res * 10 + pop; // Form the reversed number

        // Check for overflow by comparing the reversed number with its expected value after multiplication
        if (candidate / 10 != res) {
            return 0; // Return 0 if overflow occurs
        }

        res = candidate; // Update the result with the reversed number
    }

    return res; // Return the reversed integer
}

int main() {
    // Test cases to reverse integers and display the results
    cout << "Reverse of 4 is " << reverse_int(4) << endl;
    cout << "Reverse of 123 is " << reverse_int(123) << endl;
    cout << "Reverse of 208478933 is " << reverse_int(208478933) << endl;
    cout << "Reverse of -73634 is " << reverse_int(-73634) << endl;

    return 0; // Return 0 to indicate successful completion
}

Sample Output:

Reverse of 4 is 4
Reverse of 123 is 321
Reverse of 208478933 is 339874802
Reverse of -73634 is -43637

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to reverse the digits of an integer recursively and print the reversed number.
• Write a C++ program that reverses an integer by converting it to a string, then reversing the string and converting it back to an integer.
• Write a C++ program to reverse an integer without converting it to a string by using modulo and division operations in a loop.
• Write a C++ program to implement a function that reverses the digits of a number and checks if the reversed number is equal to the original (palindrome test).

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