/*
 * To print all Kaprekar numbers in the range 1 to 999.
 * Consider an n-digit positive integerr k. Square it and add the right n digits
 * to the left n or n-1 digits. If the resultant sum of either is k, then k is
 * called a Kaprekar number.

 * To be compiled using: gcc -lm
 * For example,if your filename is kaprekar.c,compile it using: gcc -lm kaprekar.c 

 * @author-Karan Narain(karan@iitk.ac.in)
 *
*/

#include <stdio.h>
#include <math.h>
//Function to count the number of digits
int num_digits(int k)
{
	int dig=0;
	while(k>0)
	{
		k=k/10;
		dig++;
	}
	return dig;

}

int isKaprekar(int k)
{
	int n,square,square_digits,sum=0,right_n,left,p;
	n=num_digits(k);
	square=pow(k,2);
	square_digits=num_digits(square);
	p=pow(10,n);
	//right n digits
	right_n=square%p;
	//if the value of right n digits is 0,then it cannot be a kaprekar number.
	//eg.square of 100 is 10000,still 100 is not a kaprekar number since the right n-digits of 10000 represent 0
	if(right_n==0)
	return 0;
	left=square/p;
	sum=(right_n + left);
	if(sum==k)
	return 1;
	//if the square has 2n-1 digits,then we should check for the sum of left n digits with the right n digits as well(there will be an overlap)
	if(square_digits==((2*n)-1))
	{
		p=pow(10,n-1);
		left=square/p;
		sum=(right_n + left );
		if(sum==k)
		return 1;
		else
		return 0;	
	}

}

int main()
{
	int i;
	printf("\nPrinting the list of Kaprekar numbers from 1 to 999...\n");
	for(i=1;i<=999;i++)
	{
		if(isKaprekar(i)==1)
		printf("%d\n",i);
	}
	return 0;
}