C program to check if a number is Strong number

A Strong number (also known as a Krishnamurthy number) is a special number whose sum of the factorials of its digits is equal to the number itself. For example, 145 is a Strong number because 1! + 4! + 5! = 1 + 24 + 120 = 145.

In this article, we will write a C program to check whether a given number is Strong. We'll begin by understanding the concept of Strong numbers, then outline the algorithm, and finally provide the complete C program with detailed explanations.

Understanding Strong Numbers

A Strong number satisfies the following condition:

Sum of the factorials of its digits=Number

For example:

• 145 is a Strong number because 1! + 4! + 5! = 145.

Algorithm to Check for a Strong Number

1. Input the number: Get the number from the user.
2. Find the factorial of each digit: Iterate through each digit of the number and find its factorial.
3. Sum the factorials: Calculate the sum of the factorials of all digits.
4. Compare the sum with the original number: If the sum equals the original number, it is a Strong number; otherwise, it is not.

Write a C program to check if a number is Strong number

Here is the complete C program to check whether a given number is a Strong number or not:

#include <stdio.h>

int main() {
    int num, originalNum, remainder, sum = 0;

    // Input the number from the user
    printf("Enter an integer: ");
    scanf("%d", &num);

    // Store the original number to compare later
    originalNum = num;

    // Calculate the sum of the factorials of each digit
    while (num > 0) {
        remainder = num % 10;

        // Calculate factorial of the remainder
        int fact = 1;
        for (int i = 1; i <= remainder; i++) {
            fact *= i;
        }

        sum += fact;
        num /= 10;
    }

    // Check if the sum of the factorials is equal to the original number
    if (sum == originalNum) {
        printf("%d is a Strong number.", originalNum);
    } else {
        printf("%d is not a Strong number.", originalNum);
    }

    return 0;
}

Output

Enter an integer: 40585
40585 is a Strong number.

Explanation of the Code

1. Input the Number:
   • scanf("%d", &num); reads the integer input from the user.
2. Store the Original Number:
   • originalNum = num; stores the original number to compare later.
3. Calculate the Sum of the Factorials of Each Digit:
   • The while loop iterates through each digit of the number.
   • remainder = num % 10; extracts the last digit.
   • The for loop calculates the factorial of the digit.
   • sum += fact; adds the factorial of the digit to the sum.
   • num /= 10; removes the last digit from the number.
4. Check for Strong Number:
   • The condition if (sum == originalNum) checks if the sum of the factorials is equal to the original number. If true, it prints that the number is a Strong number; otherwise, it states that it is not.

Example Runs

Let's look at some example runs to see how the program works:

Example 1

Enter an integer: 145
145 is a Strong number.

• Calculation: 1! + 4! + 5! = 1 + 24 + 120 = 145.

Example 2

Enter an integer: 123
123 is not a Strong number.

• Calculation: 1! + 2! + 3! = 1 + 2 + 6 = 9.

If you found this article helpful, you might also be interested in learning how to calculate factorial of a number. Check out our detailed guide below:

• C program to calculate factorial of a number