﻿ C++ : Generate and show all Kaprekar numbers less than 1000

# C++ Exercises: Generate and show all Kaprekar numbers less than 1000

## C++ Numbers: Exercise-10 with Solution

Write a program in C++ to generate and show all Kaprekar numbers less than 1000.

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()
{
cout << "\n\n Generate and show all Kaprekar numbers less than 1000: \n";
cout << " -----------------------------------------------------------\n";
cout << " The Kaprekar numbers less than 1000 are: "<<endl;
for (int i=1; i<1000; i++)
{
if (chkkaprekar(i))
{
cout << i << " ";

}

}
cout <<endl;
return 0;
}
``````

Sample Output:

``` Generate and show all Kaprekar numbers less than 1000:
-----------------------------------------------------------
The Kaprekar numbers less than 1000 are:
1 9 45 55 99 297 703 999
```

Flowchart:

C++ Code Editor:

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