Yahoo! Answers - First L's Question

#include <iostream>

int triangleFunction(int n);

int main() {
    std::cout << triangleFunction(5);
    return 0;
}

int triangleFunction(int n) {
    int result = 0;
    for (int i = 0; i <= n; i++) {
        result += i;
    }
    return result;
}