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ChrisNguyenAE's solution

to Armstrong Numbers in the C Track

Published at Oct 18 2019 · 0 comments
Instructions
Test suite
Solution

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

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

Getting Started

Make sure you have read the "Guides" section of the C track on the Exercism site. This covers the basic information on setting up the development environment expected by the exercises.

Passing the Tests

Get the first test compiling, linking and passing by following the three rules of test-driven development.

The included makefile can be used to create and run the tests using the test task.

make test

Create just the functions you need to satisfy any compiler errors and get the test to fail. Then write just enough code to get the test to pass. Once you've done that, move onto the next test.

As you progress through the tests, take the time to refactor your implementation for readability and expressiveness and then go on to the next test.

Try to use standard C99 facilities in preference to writing your own low-level algorithms or facilities by hand.

Source

Wikipedia https://en.wikipedia.org/wiki/Narcissistic_number

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you can see how others have completed the exercise.

test_armstrong_numbers.c

#include "vendor/unity.h"
#include "../src/armstrong_numbers.h"

void setUp(void)
{
}

void tearDown(void)
{
}

static void test_zero_is_an_armstrong_number(void)
{
   TEST_ASSERT_TRUE(is_armstrong_number(0));
}

static void test_single_digit_numbers_are_armstrong_numbers(void)
{
   TEST_IGNORE();               // delete this line to run test
   TEST_ASSERT_TRUE(is_armstrong_number(5));
}

static void test_there_are_no_two_digit_armstrong_numbers(void)
{
   TEST_IGNORE();
   TEST_ASSERT_FALSE(is_armstrong_number(10));
}

static void test_three_digit_number_that_is_an_armstrong_number(void)
{
   TEST_IGNORE();
   TEST_ASSERT_TRUE(is_armstrong_number(153));
}

static void test_three_digit_number_that_is_not_an_armstrong_number(void)
{
   TEST_IGNORE();
   TEST_ASSERT_FALSE(is_armstrong_number(100));
}

static void test_four_digit_number_that_is_an_armstrong_number(void)
{
   TEST_IGNORE();
   TEST_ASSERT_TRUE(is_armstrong_number(9474));
}

static void test_four_digit_number_that_is_not_an_armstrong_number(void)
{
   TEST_IGNORE();
   TEST_ASSERT_FALSE(is_armstrong_number(9475));
}

static void test_seven_digit_number_that_is_an_armstrong_number(void)
{
   TEST_IGNORE();
   TEST_ASSERT_TRUE(is_armstrong_number(9926315));
}

static void test_seven_digit_number_that_is_not_an_armstrong_number(void)
{
   TEST_IGNORE();
   TEST_ASSERT_FALSE(is_armstrong_number(9926314));
}

int main(void)
{
   UnityBegin("test/test_armstrong_numbers.c");

   RUN_TEST(test_zero_is_an_armstrong_number);
   RUN_TEST(test_single_digit_numbers_are_armstrong_numbers);
   RUN_TEST(test_there_are_no_two_digit_armstrong_numbers);
   RUN_TEST(test_three_digit_number_that_is_an_armstrong_number);
   RUN_TEST(test_three_digit_number_that_is_not_an_armstrong_number);
   RUN_TEST(test_four_digit_number_that_is_an_armstrong_number);
   RUN_TEST(test_four_digit_number_that_is_not_an_armstrong_number);
   RUN_TEST(test_seven_digit_number_that_is_an_armstrong_number);
   RUN_TEST(test_seven_digit_number_that_is_not_an_armstrong_number);

   return UnityEnd();
}

src/armstrong_numbers.c

#include "armstrong_numbers.h"

bool is_armstrong_number(unsigned int n)
{
    unsigned int sum = 0;
    unsigned int temp = n;
    int len = log10(n) + 1;
    
    while (temp/10)
    {
        sum += pow((temp%10),len);
        temp /= 10;
    }
    sum += pow(temp,len);

    if (sum == n)
    {
        return true;
    }
    else
    {
        return false;
    }
}

src/armstrong_numbers.h

#ifndef ARMSTRONG_NUMBERS
#define ARMSTRONG_NUMBERS

#include <string.h>
#include <stdbool.h>
#include <math.h>
#include <stdlib.h>

bool is_armstrong_number(unsigned int n);

#endif

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