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

Write a C program to input number from user and check whether number is Strong number or not. How to check strong numbers using loop in C programming. Logic to check strong number in C programming.



Input number: 145



Required knowledge

Basic C programming, If else, For loop, While loop, Nested loop

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

Step by step descriptive logic to check strong number.

  1. Input a number from user to check for strong number. Store this in a variable say num. Copy it to a temporary variable for calculations purposes, say originalNum = num.
  2. Initialize another variable to store sum of factorial of digits, say sum = 0.
  3. Find last digit of the given number num. Store the result in a variable say lastDigit = num % 10.
  4. Find factorial of lastDigit. Store factorial in a variable say fact.
  5. Add factorial to sum i.e. sum = sum + fact.
  6. Remove last digit from num as it is not needed further.
  7. Repeat steps 3 to 6 till num > 0.
  8. After loop check condition for strong number. If sum == originalNum, then the given number is Strong number otherwise not.

Learn more - Program to find sum of digits of number.

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;

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

    /* Copy the value of num to a temporary variable */
    originalNum = num;

    sum = 0;

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

        /* Get 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;

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

    return 0;


Enter any number to check Strong number: 145

Happy coding 😉

About Pankaj

Pankaj Prakash is the founder, editor and blogger at Codeforwin. He loves to learn new techs and write programming articles especially for beginners. He works at Vasudhaika Software Sols. as a Software Design Engineer and manages Codeforwin. In short Pankaj is Web developer, Blogger, Learner, Tech and Music lover.

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