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Armstrong number

Intro

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:

  • 9 is an Armstrong number, because 9 = 9^1 = 9
  • 10 is not an Armstrong number, because 10 != 1^2 + 0^2 = 1
  • 153 is an Armstrong number, because: 153 = 1^3 + 5^3 + 3^3 = 1 + 125 + 27 = 153
  • 154 is not an Armstrong number, because: 154 != 1^3 + 5^3 + 4^3 = 1 + 125 + 64 = 190

Task

Write some code to determine whether a number is an Armstrong number.

The Code

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#include "armstrong_numbers.h"
#include <cmath>
#include <cstdint>
#include <string>

namespace armstrong_numbers {
bool is_armstrong_number(std::uint32_t test)
{
    if(test<10)return true;
    std::string tmp=std::to_string(test);

    std::uint32_t tmp2{};
    for(auto &n:tmp)
    {
        int base=n-'0';
        tmp2+=pow(base,tmp.size());
    }
    return tmp2==test?true:false;
}
}  // namespace armstrong_numbers

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#include <cstdint>
#if !defined(ARMSTRONG_NUMBERS_H)
#define ARMSTRONG_NUMBERS_H

namespace armstrong_numbers {
bool is_armstrong_number(std::uint32_t);
}  // namespace armstrong_numbers

#endif // ARMSTRONG_NUMBERS_H
Last update: February 13, 2021

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