﻿ C++ Exercises: Check if a number is Mersenne number or not - w3resource

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:

C++ Code Editor:

What is the difficulty level of this exercise?

﻿

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