﻿ C++ : Check if a given number is a Kaprekar number or not

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

## C++ Numbers: Exercise-9 with Solution

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

Pictorial Presentation:

Sample Solution:

C++ Code :

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

bool chkkaprekar(int n)
{
if (n == 1)
return true;
int sqr_n = n * n;
int ctr_digits = 0;
while (sqr_n)
{
ctr_digits++;
sqr_n /= 10;
}
sqr_n = n*n;
for (int r_digits=1; r_digits<ctr_digits; r_digits++)
{
int eq_parts = pow(10, r_digits);

if (eq_parts == n)
continue;
int sum = sqr_n/eq_parts + sqr_n % eq_parts;
if (sum == n)
return true;
}
return false;
}
int main()
{
int kpno;
cout << "\n\n Check whether a given number is a Kaprekar number: \n";
cout << " -------------------------------------------------------\n";
cout << " Input a number: ";
cin >> kpno;
chkkaprekar(kpno)? cout << kpno <<" is a Kaprekar number. ": cout << kpno<<" is not a kaprekar number.";
cout <<endl;
}
``````

Sample Output:

``` Check whether a given number is a Kaprekar number:
-------------------------------------------------------
Input a number: 45.
45 is a Kaprekar number.
```

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