﻿ C++ Exercises: Count the Amicable pairs in an array - w3resource

# C++ Exercises: Count the Amicable pairs in an array

## C++ Numbers: Exercise-29 with Solution

Write a program in C++ to count the Amicable pairs in an array.

Sample Solution:

C++ Code :

``````#include <bits/stdc++.h>
using namespace std;

int ProDivSum(int n)
{
int sum = 1;
for (int i=2; i<=sqrt(n); i++)
{
if (n%i == 0)
{
sum += i;

// To handle perfect squares
if (n/i != i)
sum += n/i;
}
}
return sum;
}
bool chkAmicable(int a,int b)
{
return(ProDivSum(a) == b && ProDivSum(b) == a);
}
int ChkPairs(int arr[],int num1)
{
int ctr = 0;
for (int i=0; i<num1; i++)
for (int j=i+1; j<num1; j++)
if (chkAmicable(arr[i], arr[j]))
ctr++;
return ctr;
}
int main()
{
int nn;
int n, i, j, ctr;
cout << "\n\n Count the Amicable pairs in a specific array: \n";
cout << " Sample pairs : (220, 284)(1184,1210) (2620,2924) (5020,5564) (6232,6368)... \n";
cout << " ------------------------------------------------------------------------------\n";
cout << "\n Input the number of elements to be stored in the array: ";
cin>>nn;
int arr1[nn];
for(i=0;i<nn;i++)
{
cout<<"element - "<<i<<": ";
cin>>arr1[i];
}
int n1 = sizeof(arr1)/sizeof(arr1[0]);
cout <<" Number of Amicable pairs presents in the array: "<< ChkPairs(arr1, n1) << endl;
return 0;
}
``````

Sample Output:

```Count the Amicable pairs in a specific array:
Sample pairs : (220, 284)(1184,1210) (2620,2924) (5020,5564) (6232,6368)...
------------------------------------------------------------------------------

Input the number of elements to be stored in the array: 2
element - 0: 220
element - 1: 284
Number of Amicable pairs presents in the array: 1
```

Flowchart:

C++ Code Editor:

Contribute your code and comments through Disqus.

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