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C++ Exercises: Print the first 20 numbers of the Pell series

C++ Numbers: Exercise-39 with Solution

Write a program in C++ to print the first 20 numbers of the Pell series.

Sample Solution:

C++ Code :

#include <iostream>
using namespace std;
int main()
{
	int n,a=1,b=0,c;
 cout << "\n\n Find the first 20 numbers of the Pell series: \n";
 cout << " --------------------------------------------------\n";	
    cout<<" The first 20 numbers of Pell series are: "<<endl;
    c=0;
    cout<<" "<<c<<" ";
    for(n=1; n<20; n++)
     {
      c= a + 2*b;
      cout<<c<<" ";
      a = b;
      b = c;
     }
	 cout<<endl;
}

Sample Output:

Find the first 20 numbers of the Pell series:                         
 --------------------------------------------------                    
 The first 20 numbers of Pell series are:                              
 0 1 2 5 12 29 70 169 408 985 2378 5741 13860 33461 80782 195025 470832
 1136689 2744210 6625109

Flowchart:

Flowchart: Print the first 20 numbers of the Pell series

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