C program to check whether a number is Strong number or not

Write a C program to enter any number and check whether number is Strong number or not. How to check strong numbers using loop in C programming. Logic to check whether a given number is strong number or not in C program.

Input number: 145

145 is STRONG NUMBER

Required knowledge

Basic C programming, If else, For loop

Must have programming knowledge for this program.

What is Strong number?

Strong number is a special number whose sum of factorial of digits is equal to the original number. For example: 145 is strong number. Since, 1! + 4! + 5! = 145

Logic to check Strong number

Below is the step by step descriptive logic to check strong number.

1. Read a number from user which needs to be checked as strong number. Store this in some variable say num.
2. Copy the original value of num to some other variable for calculations purposes. Say originalNum = num.
3. Initialize another variable to store sum of factorial of digits. Say sum = 0.
4. Run a loop for each extracting each digit of the given number. Inside this loop extract the last digit of num, store it in some variable say lastDigit = num % 10.
5. Find factorial of lastDigit found above. Store factorial in some variable say fact.
6. Add factorial to the sum i.e. sum = sum + lastDigit.
7. Repeat steps 3-6 till num > 0.
8. After the loop check condition for strong number. If sum == originalNum, then the given number is Strong number otherwise not.

Program to check Strong number

/**
 * C program to check whether a number is Strong Number or not
 */

#include <stdio.h>

int main()
{
    int i, originalNum, num, lastDigit, sum;
    long fact;

    /*
     * Read a number from user
     */
    printf("Enter any number to check Strong number: ");
    scanf("%d", &num);

    // Copy the value of num to some other variable
    originalNum = num;

    sum = 0;

    /*
     * Calculate sum of factorial of digits
     */
    while(num > 0)
    {

        // Extract the last digit of num
        lastDigit = num % 10;

        /*
         * Find factorial of last digit
         */
        fact = 1;
        for(i=1; i<=lastDigit; i++)
        {
            fact = fact * i;
        }

        /* Add factorial to sum */
        sum = sum + fact;

        num = num / 10;
    }

    /* 
     * Strong number condition
     */
    if(sum == originalNum)
    {
        printf("%d is STRONG NUMBER", originalNum);
    }
    else
    {
        printf("%d is NOT STRONG NUMBER", originalNum);
    }

    return 0;
} 

Enter any number to check Strong number: 145
145 is STRONG NUMBER

Happy coding ;)