Strong Number in C: An In-Depth Guide


In this comprehensive guide, we will delve deep into the realm of strong number, exploring their definition, properties, and implementation in the C programming language.

Also Read : Switch Case in C Program to Calculate Area of Circle and Triangle

In the world of mathematics and programming, certain numbers possess intriguing properties and characteristics that make them stand out from the rest.

One such fascinating concept is the strong number.

A strong number, also known as a strong factorial, is a special type of number that exhibits a particular pattern when it comes to the sum of its factorial digits.

Also Read: Array of Pointers in C: A Comprehensive Guide

What is a Strong Number?

A strong number is a positive integer that possesses a distinct property related to the sum of the factorials of its individual digits.

To determine if a number is a strong number, we need to compute the factorial of each digit and sum them up.

Also Read: Static Functions in C: A Complete Guide

If the resulting sum equals the original number, then it is deemed a strong number. For instance, let’s consider the number 145:

1! + 4! + 5! = 1 + 24 + 120 = 145

As the sum of the factorials of its digits equals the original number, 145 is indeed a strong number.

Also Read: Palindrome in C using Pointers

Properties of Strong Numbers

Strong numbers exhibit several interesting properties, making them an intriguing subject for exploration.

Also Read: Also Read: Print Contents of File in Reverse Order in C

Let’s delve into some of the key properties of strong numbers:

  1. Uniqueness: Unlike prime numbers or perfect numbers, strong numbers are relatively rare and unique. They cannot be easily predicted or determined without performing the necessary calculations.
  2. Digit Factorial Sum: The defining characteristic of a strong number is the equality between the sum of the factorials of its digits and the original number itself. This property sets them apart from other types of numbers.
  3. Range: Strong numbers are bounded by the maximum value of an integer in a given programming language. In the case of the C programming language, this limit is typically defined by the size of an int variable.
  4. Existence: Strong numbers exist only within the realm of positive integers. Negative numbers and zero cannot be classified as strong numbers.
  5. Ascending Order: The digits of a strong number must be written in ascending order. This condition ensures that the sum of their factorials corresponds to the number itself.

Also Read: Floyd Triangle in C Programming

Implementation of Strong Number in C

Now that we have a good understanding of what strong numbers are and their properties, let’s explore how we can implement a program to identify and validate strong numbers using the C programming language.

Also Read: Search a Character in a String Using a Pointer in C

In this section, we will provide step-by-step instructions and code snippets to facilitate your understanding and enable you to create your own strong number checker.

Step 1: Include Necessary Header Files

Before diving into the implementation, we need to include the necessary header files for our program.

Also Read: Factorial Program in C Programming

In this case, we require the <stdio.h> and <stdbool.h> headers.

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

Step 2: Define a Function to Calculate the Factorial of a Digit

To compute the factorial of a digit, we need to define a function that takes an integer as input and returns the factorial as an integer.

Also Read: C Program To Read Two Files Simultaneously

Here’s an example implementation of the factorial function:

int factorial(int n) {
    int result = 1;
    for (int i = 2; i <= n; i++) {
        result *= i;
    return result;

Step 3: Define a Function to Check for Strong Numbers

Next, we will define a function that checks whether a given number is a strong number.

This function will take an integer as input and return a boolean value (true if the number is strong, false otherwise).

Also Read: C Program To Read Two Files Simultaneously

Here’s an example implementation of the strong number checker function:

bool isStrongNumber(int number) {
    int originalNumber = number;
    int sum = 0;

    while (number > 0) {
        int digit = number % 10;
        sum += factorial(digit);
        number /= 10;

    return (sum == originalNumber);

Step 4: Test the Strong Number Checker Function

To ensure our strong number checker function is working correctly, we can test it with various numbers.

Also Read: Swapping of Two Numbers in C

Here’s an example test function that checks a range of numbers and prints the strong numbers found:

void testStrongNumbers(int start, int end) {
    printf("Strong numbers between %d and %d:\n", start, end);
    for (int i = start; i <= end; i++) {
        if (isStrongNumber(i)) {
            printf("%d\n", i);

Step 5: Putting It All Together

To use our strong number checker, we need to call the testStrongNumbers function and provide the desired range of numbers to check.

Also Read: C Program to Find the Sum of Cubes of Elements in an Array

Here’s an example usage:

int main() {
    int start = 1;
    int end = 10000;
    testStrongNumbers(start, end);
    return 0;

Also Read: Factorial Program in C Programming

Frequently Asked Questions (FAQs)

1. Are there any negative strong numbers?

No, strong numbers are defined only for positive integers.

2. What is the largest strong number that can be represented in C?

The largest strong number that can be represented in C is dependent on the maximum value of an integer in the specific C implementation you’re using.

3. Can a strong number have leading zeros?

No, a strong number cannot have leading zeros. The digits must be written in ascending order.

4. How can I optimize the strong number checker algorithm?

One optimization technique is to precompute the factorials of digits from 0 to 9 and store them in an array for quick access during the calculation.

5. Are there any real-world applications for strong numbers?

While strong numbers don’t have direct practical applications, they serve as a fascinating mathematical concept and can be used for educational purposes or as programming exercises.

6. Are there any famous strong numbers?

There are a few notable strong numbers, such as 145, 40585, and 871.

Also Read: C Program to Display a String in Capital Letters


In this comprehensive guide, we explored the captivating concept of strong numbers in the context of the C programming language.

We learned that strong numbers possess unique properties, such as the equality between the sum of their factorial digits and the original number itself.

Also Read: Getchar and Putchar Function in C with Example

By following the step-by-step implementation guide, you can now create your own strong number checker in C and dive further into the intriguing world of numbers and mathematics.

Remember, understanding strong numbers not only expands your mathematical knowledge but also enhances your problem-solving skills and programming expertise.

Also Read: 25 Tricky Questions on Pointers in C: Explained and Answered

So go ahead, embrace the power of strong numbers, and unleash your mathematical prowess!