Hey. I want to write a program that approximates the value of PI using the Taylor Series. This is the program I've written so far but I'm not sure how to complete the FOR loop. Someone please help.

Code:
#include <cstdlib>
#include <iostream>


using namespace std;


int main(int argc, char *argv[])
{
    cout<<"Piapproximation\n"
    "Welcome to my version of Piapproximation\n";
    //declaring variables
    int terms;
    double pi = 0.0;
    //getting input from user
    cout<<"\nEnter the number of terms: ";
    cin>> terms;
    //loop to calculate the value of pi
    for (long int i = 1; i <= terms; i ++) 
    ...
    //output 
    cout<<"\nThe approximation of PI is: "<< pi <<
    "\n\nThank you!\n";
    
    system("PAUSE");
    return EXIT_SUCCESS;
}