// Functions can call themselves.
// This is called recursion.

#include <iostream>
#include <cstdlib>
using namespace std;

int triangular_number( int n )
{
    if ( n == 1 )
        return( 1 );
    else
        return( n + triangular_number( n-1 ) );  // Functions calls itself!
}

int main()
{
    char choice; int n;
    
    do {
        cout << "Enter a positive integer: ";
        cin >> n;
        cout << "T(" << n << ") = " << triangular_number( n ) << endl;
        cout << "Run again? (y=yes) ";
        cin >> choice;
    } while( choice == 'y' || choice == 'Y' );
    
    cout << "\n\n"; system( "PAUSE" );
    return( EXIT_SUCCESS );
}