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C++ Exercises: Check if a number is Mersenne number or not

C++ Numbers: Exercise-35 with Solution

Write a program in C++ to check if a number is Mersenne number or not.

Sample Solution:

C++ Code :

# include <iostream>
# include <math.h>
using namespace std;
int main()
{
    int n,p,ans,i,n1;
	double result;
	cout << "\n\n Check whether a given number is Mersenne number or not:\n";
	cout << "------------------------------------------------------------\n";
	cout << " Input a number: ";
    cin>>n;
    n1=n+1;
        p = 0;
        ans = 0;
        for(i=0;;i++)
        {
            p=(int)pow(2,i);
            if(p>n1)
            {
                break;
            }
            else if(p==n1)
            {
               cout<<" "<<n<<" is a Mersenne number."<<endl;
               ans=1;
            }
        }
  if(ans==0)
  {
   cout<<" "<<n<<" is not a Mersenne number."<<endl;
  }	
}

Sample Output:

 Check whether a given number is Mersenne number or not:               
------------------------------------------------------------           
 Input a number: 31                                                    
 31 is a Mersenne number.  

Flowchart:

Flowchart: Check if a number is Mersenne number or not

C++ Code Editor:

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Previous: Write a program in C++ to find any number between 1 and n that can be expressed as the sum of two cubes in two (or more) different ways.
Next: Write a program in C++ to generate Mersenne primes within a range of numbers.

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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