C++ Armstrong Number Program

An Armstrong number equals the sum of its digits, each raised to the power of the number of digits. For example 153 = 1^3 + 5^3 + 3^3.

Program

#include <iostream>
#include <string>

int power(int base, int exponent) {
    int result = 1;
    for (int i = 0; i < exponent; i++) result *= base;
    return result;
}

bool is_armstrong(int number) {
    int digits = static_cast<int>(std::to_string(number).size());
    int sum = 0, n = number;
    while (n > 0) {
        sum += power(n % 10, digits);
        n /= 10;
    }
    return sum == number;
}

int main() {
    std::cout << std::boolalpha << is_armstrong(153) << ' ' << is_armstrong(154) << ' ' << is_armstrong(9474) << '\n';

    std::cout << "Armstrong numbers up to 1000: ";
    for (int i = 1; i <= 1000; i++) {
        if (is_armstrong(i)) std::cout << i << ' ';
    }
    std::cout << '\n';
}

How it works

• std::to_string(number).size() counts the digits.
• The loop takes the last digit with % 10 and adds its power.
• We wrote our own integer power, because std::pow works with decimals and can give a small rounding error.

Related: C++ while Loop.

• Previous Code
• Next Code

---

Tutorials
No Content Found.

Exercises & Assignments
No Content Found.

Interview Questions & Answers
No Content Found.