﻿ C++ : Perfect numbers and count number between 1 to 1000

# C++ Exercises: Find Perfect numbers and number of Perfect numbers between 1 to 1000

## C++ Numbers: Exercise-5 with Solution

Write a program in C++ to find Perfect numbers and number of Perfect numbers between 1 to 1000.

Pictorial Presentation:

Sample Solution:

C++ Code :

``````# include <iostream>
# include <string>
using namespace std;
int main()
{
int i=1, u=1, sum=0,ctr=0;
cout << "\n\n Find the Perfect numbers and number of Perfect numbers between 1 to 1000:\n";
cout << "------------------------------------------------------------------------------\n";
cout << "The Perfect numbers are : \n";
while(i<=1000)
{
while(u<=1000)
{
if(u<i)
{
if(i%u==0 )
sum=sum+u;
}
u++;
}
if(sum==i)
{
ctr++;
cout<<i<<" is a Perfect number."<<"\n";
}
i++;
u=1;  sum=0;
}
cout<<"Number of Perfect numbers between 1 to 1000 is: "<<ctr<<"\n";
}
``````

Sample Output:

``` Find the Perfect numbers and number of Perfect numbers between 1 to 1000:
------------------------------------------------------------------------------
The Perfect numbers are :
6 is a perfect number.
28 is a perfect number.
496 is a perfect number.
Number of perfect numbers between 1 to 1000 is: 3
```

Flowchart:

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