Tutoring: demo of using loops to get user input from cin

looping.cpp

#include <iostream>

using namespace std;

int main()
{

  double miles;
  
  cout << "Enter miles:" << endl;
  cin >> miles;
  
  cout << 100 / miles << endl; 
  // Problem: In the code above, the user might give us a bad number (e.g. 0 or -100) that produces bad results. 
  // How can we prevent this?
  // Answer: looping.

  // There are three types of loops in C++. 
  
  // For loop - This loop will execute five times. This is not useful (for this problem): how can we be sure the 5th time is the right number?
  for(int i=0; i < 5; i++)
  {
    cout<<"Enter miles:" << endl;
    cin >> miles;
  }
  
  cout << 100 / miles << endl; 
  
  
  // While loop - this will execute until the user gives a correct input. 
  cout<<"Enter miles:" << endl;
  cin >> miles;
  
  while(miles <= 0)
  {
    cout<<"Miles must be greater than zero."<<endl;
    cout<<"Enter miles:"<<endl;
    cin >> miles;
  }
  
  cout << 100 / miles << endl; 

  // Do-While loop - notice how the the While-loop example above, we had to repeat the same code twice to make it work. 
  // The Do-While loop is useful when you always need to run a piece of code at least once, maybe more.
	do{
		cout << "Enter miles:" << endl;
		cin >> miles;

		if (miles < 0)
			cout << "Miles must be > 0." << endl;

	}  while (miles < 0);

  cout << 100 / miles << endl; 
  
  

	system("pause");

	return 0;
}