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C++ Exercises: Generate Mersenne primes within a range of numbers

C++ Numbers: Exercise-36 with Solution

Write a program in C++ to generate Mersenne primes within a range of numbers.

Sample Solution:

C++ Code :

#include<bits/stdc++.h>
using namespace std;
 
void GenAllPrim(int n1, bool prarr1[])
{
    for (int i=0; i<=n1; i++)
        prarr1[i] = true;
 
    for (int p=2; p*p<=n1; p++)
    {
        if (prarr1[p] == true)
        {
            for (int i=p*2; i<=n1; i += p)
                prarr1[i] = false;
        }
    }
}
void chkMerPrime(int nm)
{
    bool prarr1[nm+1];
    GenAllPrim(nm,prarr1);
    for (int j=2; ((1<<j)-1) <= nm; j++)
    {
        long long num = (1<<j) - 1;
        if (prarr1[num])
            cout <<" "<< num << " ";
    }
}
int main()
{
    int n ;
	cout << "\n\n Generate Mersenne primes within a range of numbers:\n";
	cout << "--------------------------------------------------------\n";
	cout << " Input a upper limit [range from 1 to upper limit]: ";
    cin>>n;	
    cout << " Mersenne prime numbers are: "<<endl;
    chkMerPrime(n);
    cout<<endl<<endl;
}

Sample Output:

Generate Mersenne primes within a range of numbers:                   
--------------------------------------------------------               
 Input a upper limit [range from 1 to upper limit]: 200                
 Mersenne prime numbers are:                                           
 3  7  31  127 

Flowchart:

Flowchart: Generate mersenne primes within a range of numbers
Flowchart: Generate mersenne primes within a range of numbers
Flowchart: Generate mersenne primes within a range of numbers

C++ Code Editor:

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Previous: Write a program in C++ to check if a number is Mersenne number or not.
Next: Write a program in C++ to find Narcissistic decimal numbers within a specific range.

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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