C Exercises: Find the happy numbers between 1 to 1000

Last update on August 05 2025 12:55:47 (UTC/GMT +8 hours)

14. Happy Numbers Between 1 and 1000 Variants

Write a program in C to find the happy numbers between 1 and 1000.

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 j, ctr;
    printf("\n\n Find the Happy numbers between 1 to 1000: \n");
    printf(" ----------------------------------------------\n");
    printf(" The happy numbers between 1 to 1000 are: ");

    // Check for Happy numbers in the range of 1 to 1000
    for (j = 1; j <= 1000; j++)
    {
        if (checkHappy(j)) // If j is a Happy number
            printf("%d ", j); // Print the Happy number
    }
    printf("\n");
    return 0;
}

Sample Output:

 The happy numbers between 1 to 1000 are: 1 7 10 13 19 23 28 31 32 44 49.....

Visual Presentation:

C programming: Find the happy numbers between 1 to 1000.

Flowchart:

For more Practice: Solve these Related Problems:

Write a C program to list all happy numbers between two user-specified limits.
Write a C program to count and display happy numbers in a given range.
Write a C program to generate happy numbers and plot their frequency distribution.
Write a C program to optimize the detection of happy numbers with caching techniques.

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