C Exercises: Check whether a given number is a Kaprekar number or not

Last update on October 16 2025 11:05:02 (UTC/GMT +8 hours)

6. Kaprekar Number Check Variants

Write a program in C to check whether a given number is a Kaprekar number or not.

Test Data
Input a number: 45

Sample Solution:

C Code:

#include <stdio.h>
#include <stdbool.h>
#include <math.h>

// Function to check if a number is a Kaprekar number
bool chkkaprekar(int n) {
    if (n == 1)
        return true; // If the number is 1, it's considered a Kaprekar number

    int sqr_n = n * n; // Square of the number
    int ctr_digits = 0; // Counter for the number of digits in the square

    // Count the number of digits in the square of the number
    while (sqr_n) {
        ctr_digits++;
        sqr_n /= 10;
    }

    sqr_n = n * n; // Reset the square of the number

    // Loop to check for Kaprekar property
    for (int r_digits = 1; r_digits < ctr_digits; r_digits++) {
        int eq_parts = pow(10, r_digits); // Calculate the divisor for splitting the square

        if (eq_parts == n)
            continue; // Skip when the divisor equals the number itself

        // Calculate the sum of the split parts of the square
        int sum = sqr_n / eq_parts + sqr_n % eq_parts;

        if (sum == n)
            return true; // If the sum of split parts equals the number, it's a Kaprekar number
    }

    return false; // If the conditions aren't met, it's not a Kaprekar number
}

// Main function
int main() {
    int kpno;
    printf("\n\n Check whether a given number is a Kaprekar number: \n");
    printf(" -------------------------------------------------------\n");
    printf(" Input a number: ");
    scanf("%d", &kpno); // Read an integer from the user and store it in 'kpno'

    // Check if the number is a Kaprekar number and print the result
    if (chkkaprekar(kpno) == true) {
        printf("%d is a Kaprekar number. \n", kpno);
    } else {
        printf("%d is not a Kaprekar number. \n", kpno);
    }

    return 0;
}

Sample Output:

 Input a number: 45                                                                                           
45 is a Kaprekar number. 

Visual Presentation:

Flowchart:

For more Practice: Solve these Related Problems:

• Write a C program to verify Kaprekar numbers using string manipulation for splitting squares.
• Write a C program to check if a number is Kaprekar by testing different square splits.
• Write a C program to list Kaprekar numbers along with details of their split parts.
• Write a C program to test the Kaprekar property for large numbers using high-precision arithmetic.

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