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

//Topic: Passing by reference

//change value of given first variable to become num1*num2.
void multiplyBy(double &num1, double num2)
{
	num1 = num1 * num2;

	//for fun... won't change variable from main
	num2 = -999;
}


//Increase value of num1 by value of num2.
//(but num2 shoudlnt' change...)
//So, pass num1 by reference (so we can change it)
//But don't need to pass num2 by reference (since it isn't supposed to change)
//So we'll pass num2 by value
void increaseBy(int &num1, int num2)
{
	num1 = num1 + num2;
}

//make given char variable to be
//the capital version of itself
void makeCapital(char &letter)
{
	letter = letter - 32;
}

//return true if n is prime
//return false if n is not prime
//How efficient is this?
//run time is: O( sqrt(n) )
bool isPrime(int n)
{
	for (int i = 2; i < sqrt(n); i++)
	{
		if (n % i == 0) //modulus operator
		{
			return false;
		}
	}
	return true;
}


int main()
{
	//Review passing by reference
	double x = 7;
	double y = 3.14;
	multiplyBy(x, y);

	cout << x << endl; //should be 7*3.14
	cout << y << endl; //should still be 3.14

	int z = 53;
	increaseBy(z, 21);

	cout << z << endl; //74
	increaseBy(z, 5);
	cout << z << endl; //79

	char letter2 = 'd';
	makeCapital(letter2);
	cout << letter2 << endl; // D

	//uh oh, let's do something bad..
	letter2 = 'R';
	makeCapital(letter2);
	cout << letter2 << endl; // ???

	//Let's implement isPrime(n)
	cout << isPrime(9) << endl; //false
	cout << isPrime(5) << endl; //true
	cout << isPrime(77) << endl; //false
	cout << isPrime(163) << endl; //true

	listPrimes(100);


	return 0;
}