C Exercises: Display and count the number of Lychrel numbers within a specific range.

Last update on March 19 2025 12:39:20 (UTC/GMT +8 hours)

9. Lychrel Numbers in a Range Variants

Write a program in C to display and count the number of Lychrel numbers within a specific range (from 1 to a specific upper limit).

Test Data
Input the upper limit: 1000

Sample Solution:

C Code:

#include <stdio.h> // Include standard input-output library
#include <stdbool.h> // Include library for boolean type
#include <stdlib.h> // Include standard library
// Function to check if a number is a palindrome

// Function prototypes
bool palindrome(unsigned long long int i); // Function to check if a number is a palindrome
unsigned long long int reverse(unsigned long long int i); // Function to reverse a number
bool lychrel(unsigned long long int i); // Function to check if a number is a Lychrel number

int main(void) {
    unsigned long long int i = 0; // Declare and initialize variable for input number
    int count = 0, ulmt; // Declare variables for count and upper limit
    printf("\n\n Display and count number of Lychrel numbers within a specific range: \n"); // Print message
    printf(" -------------------------------------------------------------------------\n"); // Print separator
    printf(" Input the upper limit: "); // Prompt user for input
    scanf("%d", &ulmt); // Read upper limit from user
    printf("\n The Lychrel numbers are:  \n"); // Print message
    for (i = 1; i < ulmt; i++) { // Loop through numbers up to upper limit
        if (lychrel(i)) { // Check if the number is a Lychrel number
            printf(" %llu ", i); // Print the Lychrel number
            count++; // Increment count
        }
    }
    printf("\n The number of  Lychrel numbers are:  %d\n\n", count); // Print the count of Lychrel numbers
    return 0; // Return 0 to indicate successful execution
}

// Function to check if a number is a Lychrel number
bool lychrel(unsigned long long int i) {
    int j; // Declare variable for iteration counter
    bool lychrel = true; // Initialize variable to store Lychrel property
    i = i + reverse(i); // Add the input number to its reverse
    for (j = 1; j <= 30; j++) { // Loop up to 30 iterations
        if (palindrome(i)) { // Check if the result is a palindrome
            lychrel = false; // If palindrome found, set lychrel to false
            break; // Exit the loop
        }
        i = i + reverse(i); // Add the number to its reverse for the next iteration
    }
    return lychrel; // Return the Lychrel property
}

// Function to reverse a number
unsigned long long int reverse(unsigned long long int i) {
    unsigned long long int ret = 0; // Declare and initialize variable to store reversed number
    while (i != 0) { // While loop to reverse the number
        ret *= 10; // Multiply ret by 10
        ret += i % 10; // Add the last digit of i to ret
        i /= 10; // Remove the last digit of i
    }
    return ret; // Return the reversed number
}

// Function to check if a number is a palindrome
bool palindrome(unsigned long long int i) {
    return (i == reverse(i)); // Return true if i is equal to its reverse, otherwise return false
}

Sample Output:

 Input the upper limit: 1000                                                                                  
                                                                                                              
 The Lychrel numbers are:                                                                                     
 196  295  394  493  592  689  691  788  790  879  887  978  986                                              
 The number of  Lychrel numbers are:  13

Visual Presentation:

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to list all suspected Lychrel numbers between two bounds.
• Write a C program to count Lychrel numbers within a user-defined interval and output the total.
• Write a C program to check each candidate’s reverse-add sequence and print the iteration steps.
• Write a C program to filter and display Lychrel numbers from an array using optimized loops.

C Programming Code Editor:

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