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C++ Exercises: Check whether a given number is Perfect or not

C++ Numbers: Exercise-4 with Solution

Write a program in C++ to check whether a given number is Perfect or not.

Pictorial Presentation:

C++ Exercises: Check whether a given number is Perfect or not

Sample Solution:

C++ Code :

# include <iostream>
# include <string>
using namespace std;
int main()
{
    int i=1, u=1, sum=0,n;
 cout << "\n\n Check whether a given number is a Perfect number:\n";
 cout << "------------------------------------------------------\n";
cout << "Input a number: ";
cin >> n;
   while(u<=n)
   {                              
     if(u<n)
     {
      if(n%u==0 )
      sum=sum+u;
     }                         
     u++;
   }                           
   if(sum==n)
   {
    cout<<n<<" is a Perfect number."<<"\n";
   }
   else
   {
     cout<<n<<" is not a Perfect number."<<"\n";  
   }
}

Sample Output:

 Check whether a given number is a Perfect number:                                                   
------------------------------------------------------                                               
Input a number: 28                                                                                   
28 is a Perfect number.

Flowchart:

Flowchart: Check whether a given number is Perfect or not

C++ Code Editor:

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Previous: Write a program in C++ to find the Abundant numbers (integers) between 1 to 1000.
Next: Write a program in C++ to find Perfect numbers and number of Perfect numbers between 1 to 1000.

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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