C++ Exercises: Check whether a number is Lychrel number or not

Last update on April 12 2025 13:00:03 (UTC/GMT +8 hours)

11. Lychrel Number Check

Write a program in C++ to check whether a number is a Lychrel number or not.

Visual Presentation:

Sample Solution:

C++ Code :

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

// Function to reverse a number
long long int numReverse(long long int number)
{
    long long int rem = 0;
    while (number > 0)
    {
        rem = (rem * 10) + (number % 10); // Extract digits in reverse order
        number = number / 10; // Remove the last digit
    }
    return rem; // Return the reversed number
}

// Function to check if a number is a palindrome
bool is_Palindrome(long long int num)
{
    return (num == numReverse(num)); // Check if the number is equal to its reverse
}

// Function to check if a number is a Lychrel number
bool isLychrel(int num, const int iterCount = 500)
{
    long long int temp = num;
    long long int rev;
    for (int i = 0; i < iterCount; i++)
    {
        rev = numReverse(temp); // Get the reversed number
        if (is_Palindrome(rev + temp)) // Check if the sum of the number and its reverse is a palindrome
            return false; // If it's a palindrome, it's not a Lychrel number
        temp = temp + rev; // Update temp with the sum
    }
    return true; // If after iterations no palindrome is found, it's a Lychrel number
}

int main()
{
    int lyno;
    bool l;
    cout << "\n\n Check whether a given number is a Lychrel number: \n"; // Display a message for user
    cout << " ------------------------------------------------------\n";
    cout << " Input a number: ";
    cin >> lyno; // Input a number from the user

    l = isLychrel(lyno); // Check if the input number is a Lychrel number

    if (l == false)
    {
        cout << " The number is not a Lychrel number." << endl; // Display result if it's not a Lychrel number
    }
    else
    {
        cout << " The number is a Lychrel number." << endl; // Display result if it's a Lychrel number
    }
    return 0; // End of the program
}

Sample Output:

Check whether a given number is a Lychrel number:                                                   
 ------------------------------------------------------                                              
 Input a number: 196                                                                                 
 The number is a Lychrel number.

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C++ program to determine if a number is a Lychrel candidate by iterating digit reversals with a limit.
• Write a C++ program to check for Lychrel numbers using string reversal and loop counters.
• Write a C++ program to test if a number is Lychrel by comparing iterative sums to the original number.
• Write a C++ program to verify Lychrel numbers using recursion with a set maximum number of iterations.

C++ Code Editor:

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