C++ Program to Check Armstrong Number

Posted in C++ Tutorial

Updated on Jan 11, 2024

By Mari Selvan

👁️ 139 - Views

⏳ 4 mins

💬 1 Comment

Photo Credit to CodeToFun

🙋 Introduction

In the realm of programming, solving mathematical problems is a common task. One such interesting problem is checking whether a given number is an Armstrong number.

Armstrong numbers, also known as narcissistic numbers or pluperfect digital invariants, are numbers that are the sum of their own digits each raised to the power of the number of digits.

In this tutorial, we will explore a C++ program designed to check whether a given number is an Armstrong number. The program involves calculating the sum of the digits raised to the power of the number of digits and comparing it with the original number.

📄 Example

Let's delve into the C++ code that accomplishes this task.

armstrongNumber.cpp

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#include <iostream>

#include <cmath>

class ArmstrongNumber {
  public:
    // Function to check if a number is an Armstrong number
    static bool isArmstrong(int number) {
      int originalNumber = number;
      int n = 0;
      int result = 0;

      // Count the number of digits
      while (originalNumber != 0) {
        originalNumber /= 10;
        n++;
      }

      // Reset originalNumber to the actual number
      originalNumber = number;

      // Calculate the sum of nth power of individual digits
      while (originalNumber != 0) {
        int remainder = originalNumber % 10;
        result += pow(remainder, n);
        originalNumber /= 10;
      }

      // Check if the result is equal to the original number
      return result == number;
    }
};

// Driver program
int main() {
  // Replace this value with the number you want to check
  int number = 153;

  // Call the function to check if the number is Armstrong
  if (ArmstrongNumber::isArmstrong(number))
    std::cout << number << " is an Armstrong number." << std::endl;
  else
    std::cout << number << " is not an Armstrong number." << std::endl;

  return 0;
}

💻 Testing the Program

To test the program with different numbers, modify the value of number in the main function.

Output

153 is an Armstrong number.

🧠 How the Program Works

The program defines a class ArmstrongNumber containing a static method isArmstrong that takes an integer number as input and checks whether it is an Armstrong number.
Inside the main function, replace the value of number with the desired number you want to check.
The program calls the isArmstrong method and prints the result.

📏 Between the Given Range

Let's dive into the C++ code that checks for Armstrong numbers in the specified range.

isArmstrong.cpp

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#include <iostream>
#include <cmath>

// Function to check if a number is an Armstrong number
bool isArmstrong(int number) {
  int originalNumber = number;
  int numDigits = static_cast < int > (log10(number)) + 1;
  int sum = 0;

  while (number > 0) {
    int digit = number % 10;
    sum += static_cast < int > (pow(digit, numDigits));
    number /= 10;
  }

  return (sum == originalNumber);
}

// Driver program
int main() {
  std::cout << "Armstrong numbers in the range 1 to 50:\n";

  for (int i = 1; i <= 50; ++i) {
    if (isArmstrong(i)) {
      std::cout << i << " ";
    }
  }

  std::cout << std::endl;

  return 0;
}

💻 Testing the Program

Output

Armstrong numbers in the range 1 to 50:
1, 2, 3, 4, 5, 6, 7, 8, 9,

Compile and run the program to see the Armstrong numbers in the range from 1 to 50.

🧠 How the Program Works

The program defines a function isArmstrong that checks if a given number is an Armstrong number.
Inside the function, it calculates the number of digits in the given number and then iterates through each digit, raising it to the power of the number of digits.
The main function tests the range from 1 to 50, calling the isArmstrong function for each number and printing the Armstrong numbers found.

🧐 Understanding the Concept of Armstrong Number

Before delving into the code, let's understand the concept behind Armstrong numbers. An Armstrong number is a number that is the sum of its own digits each raised to the power of the number of digits.

For example, 153 is an Armstrong number because 1^3 + 5^3 + 3^3 = 153.

🎢 Optimizing the Program

While the provided program is straightforward, consider exploring and implementing alternative approaches or optimizations for checking Armstrong numbers.

Feel free to incorporate and modify this code as needed for your specific use case. Happy coding!