C Exercises: Check a number is a Happy or not

Last update on August 05 2025 12:55:10 (UTC/GMT +8 hours)

13. Happy Number Check Variants

Write a program in C to determine whether a number is Happy or not.

Test Data
Input a number: 13

Sample Solution:

C Code:

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

// Function to calculate the sum of squares of digits of a number
int SumOfSquNum(int givno)
{
    int SumOfSqr = 0;
    // Calculate the sum of squares of digits
    while (givno)
    {
        SumOfSqr += (givno % 10) * (givno % 10); // Square each digit and add to the sum
        givno /= 10; // Move to the next digit
    }
    return SumOfSqr; // Return the sum of squares of digits
}

// Function to check if a number is a Happy number
bool checkHappy(int chkhn)
{
    int slno, fstno;
    slno = fstno = chkhn;

    // Detect a cycle or if the number reaches 1
    do
    {
        slno = SumOfSquNum(slno); // Calculate the sum of squares of digits for slno
        fstno = SumOfSquNum(SumOfSquNum(fstno)); // Calculate the sum of squares of digits twice for fstno
    }
    while (slno != fstno); // Continue until both numbers meet or 1 is reached

    return (slno == 1); // If slno becomes 1, the number is a Happy number
}

// Main function
int main()
{
    int hyno;
    printf("\n\n Check whether a number is a Happy number or not: \n");
    printf(" ---------------------------------------------------\n");
    printf(" Input a number: ");
    scanf("%d", &hyno); // Input a number

    // Check if the input number is a Happy number and print the result
    if (checkHappy(hyno))
        printf("%d is a Happy number.\n", hyno);
    else
        printf("%d is not a Happy number.\n", hyno);

    return 0;
}

Sample Output:

 Input a number: 13                                                                                           
13 is a Happy number.

Visual Presentation:

C programming: Check a number is a Happy or not.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to determine if a number is happy using cycle detection techniques.
Write a C program to find happy numbers in a given range and display their iteration sequences.
Write a C program to check happiness using a hash table to record previously seen sums.
Write a C program to compare the happiness of a number in different numerical bases.

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