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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:

Flowchart: Check whether a given number is an armstrong number or not

C++ Code Editor:

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Previous: Write a program in C++ to create the first twenty Hamming numbers.
Next: Write a program in C++ to find the Armstrong number for a given range of number.

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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