﻿ C++ : Check if a number is an Armstrong number or not

C++ Exercises: Check whether a given number is an Armstrong number or not

C++ Numbers: Exercise-43 with Solution

Write a C++ program to check whether a given number is an Armstrong number or not.

/*When the sum of the cube of the individual digits of a number
is equal to that number, the number is called Armstrong number. For example 153.
Sum of its divisor is 13 + 53;+ 33; = 1+125+27 = 153*/

Sample Solution:

C++ Code:

``````#include <iostream>
using namespace std;

int main()
{
int num, r, sum = 0, temp;
cout << "\n\n Check whether a given number is an Armstrong number or not :\n";
cout << "-----------------------------------------------------------------\n";
cout << " Input a number: ";
cin >> num;
for (temp = num; num != 0; num = num / 10)
{
r = num % 10;
sum = sum + (r * r * r);
}
if (sum == temp)
cout << temp << " is an Armstrong number." << endl;
else
cout << temp << " is not an Armstrong number." << endl;
}
``````

Sample Output:

```Check whether a given number is an Armstrong number or not:
-------------------------------------------------------
Input a number: 153
153 is an Armstrong number
```

Flowchart:

C++ Code Editor:

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C++ Programming: Tips of the Day

How to use the PI constant in C++?

On some (especially older) platforms (see the comments below) you might need to

#define _USE_MATH_DEFINES and then include the necessary header file:
`#include<math.h>`

and the value of pi can be accessed via:

`M_PI`

In math.h (2014) it is defined as:

`# define M_PI           3.14159265358979323846  /* pi */`

but check your math.h for more. An extract from the "old" math.h (in 2009):

```/* Define _USE_MATH_DEFINES before including math.h to expose these macro
* definitions for common math constants.  These are placed under an #ifdef
* since these commonly-defined names are not part of the C/C++ standards.
*/```

However:

1. on newer platforms (at least on my 64 bit Ubuntu 14.04) I do not need to define the _USE_MATH_DEFINES
2. On (recent) Linux platforms there are long double values too provided as a GNU Extension:
`# define M_PIl          3.14159265358979323846`

Ref: https://bit.ly/3G4BgzQ