Calculates cosine using series expansion

cosine.cpp

//This program gets an angle in radians and calculates its cosine using series expansion.

#include<iostream>
#include<cmath>
using namespace std;
//declare variables and functions here
double angle;
double cosx=1;
//cosine function uses first five terms of series expansion to return the approximate cosine of an angle.
//fact function computes factorial as seen in class.
int fact(int input){
	if (input <= 1){
	return 1;}
	else {
	return input*fact(input-1);
	}
}
double cosine(double angle){
//For loop iterates over 2, 4, 6, 8, 10.
	for(int i=2; i<=10; i+=2){
//Term variable stores number from one term of sequence
		double term = pow(angle, i)/fact(i);
//every other term is either added or subtracted.
		if(i%4==0){
		cosx = cosx + term;}
		else{
			cosx = cosx - term;}
	}
	return cosx;
	}

int main(){
//While loop lets program run indefinitely
	while(1==1){
	cout<<"please type an angle in radians"<<endl;
	cin>>angle;	
//calls series expansion cosine and prints it.
	cout<<"the series expansion cosine of that is: "<<cosine(angle)<<endl;
//Calls cmath cosine and prints that as well.
	cout<<"the c++ cosine of that angle is: "<<cos(angle)<<endl;
//In windows command prompt, CTRL-C stops a program.
	cout<<"use <CTRL-C> to quit this program"<<endl;
	}
return 0;
}