//
// example of recursion:
//
//	function to compute element of Pascal's triangle
//
// main (test) program repeatedly prompts for inputs
//
#include <iostream.h>

// precondition:  r >= 1, i <= r
// postcondition:  returns i-th element of r-th row of Pascal's 
//	triangle, where indices of both rows and elements start
//	with 1
int pascalTE(const int r, const int i);

// ---- main program ----

int main()
{
	int r, i;
	char prompt[] = "Enter row number (positive) and "
		"element number (positive, <= row number),\n"
		"or ctrl-D to end:\n";
	cout << prompt;
	while (cin >> r >> i)
	{
		if (r <= 0)
			cout << "Row number must be non-negative!\n";
		else if ((i <= 0) || (i > r))
			cout << "Element number must be non-negative "
				<< "and <= r!\n";
		else
			cout << "element " << i << " of row " << r 
				<< " is " << pascalTE(r, i) << endl;
		cout << prompt;
	}
	return 0 ;
}

// ---- function definition ----

int pascalTE(const int r, const int i)
{
	if ((i == 1) || (i == r))
		return 1;
	else
		return pascalTE(r-1, i-1) + pascalTE(r-1, i);
}