Handout - Two Common Uses for Loops

• Giving the user control over the number of times a calculation is performed.

  
  	EXAMPLE:
  
  	/* Calculate the length of a line segment, for as many
  	   pairs of coordinates as the user wants to enter     */
  
  	float x1, y1, x2, y2;
  	float length;
  	char response;
  
  	response = 'Y';		/* priming the loop */
  	while (response == 'Y')
  	{
  	  cout << "Enter first pair of coordinates:  ";
  	  cin >> x1 >> y1;
  
  	  cout << "Enter second pair of coordinates:  ";
  	  cin >> x2 >> y2;
  	  
  	  length = sqrt ( (x2-x1) * (x2-x1) + (y2-y1) * (y2-y1));
  	  cout << "Length of segment is " << length << endl;
  
  	  cout << "Do you want to calculate the length of another segment?";
  	  cout << endl << "(Y or N):  ";
  	  cin >> response;
  	}
  
  	cout << "Program over" << endl;
  
  

• Repeatedly prompting for input until the user enters the input data correctly.

  	EXAMPLE:
  
  	/* loop to check for valid user input */
  
  	cout << "Enter a non-zero value for denominator:  ";
  	cin >> denominator;
  
  	while (denominator == 0)
  	{
  	  cout << "Denominator must be non-zero!" << endl;
  	  cout << "Try again." << endl;
  
  	  cout << "Enter a non-zero value for denominator:  ";
  	  cin >> denominator;
  	}
  
  	quotient = numerator/denominator;