long double = crash?!?

[iggi]

I have this program, it works for MOST numbers entered, but once I enter "123456", the program just exits. Here is my source code:

#include <iostream>

using namespace std;

long double function(int n);
int n;

int main() {
while(1) {
    cout << "enter n for computing F(n) (-1 to exit): ";
    cin >> n;
    cout << 2*function(n) << "\n";
    if (n == -1) 
    break;
}
return 0;
}

long double function(int n) {
    if ( n <= 0)
    return 0;
    else
    return n+function(n-1);
}

This program calculates F(n)= 2(1) + 2(2) + ... + 2n.

[magicalblender]

when you enter 123456, function() is recursively called 123456 times, which is too much. You might want to just use a while loop instead.

[iggi]

the question posed to me stated I must specifically use recursion.

[magicalblender]

Some compilers are able to optimize tail-recursion functions, like yours, so that they don't cause stack overflows. Check to see if your compiler has such an option, or find another compiler that does.