CS 202 Fall 2013
In-Class Challenge for Tuesday, November 5, 2013

Our Goal

We wish to write a class template WaitInLine. This keeps track of a “line”, like the one for a cash register at a store. You enter the line at the back and exit at the front, so that people exit the line in the same order they entered.

An object of class WaitInLine<T> should keep track of a “line” of items of type T. I will refer to type T as the value type.

WaitInLine should have three public member functions.

• put. Take a value whose type is the value type. Returns nothing. Enters its parameter at the back of the line.
• get. Takes no parameters. Returns the value type. Removes the value at the front of the line and returns it.
• empty. Takes no parameters. Returns bool. Returns true if there are no items in the line; otherwise returns false.

In addition, WaitInLine should have a default constructor. However, there is a good chance that you do not need to write it.

Example usage:

[C++]

WaitInLine<int> w;

bool b1 = w.empty();                  // Should be true
w.put(8);
bool b2 = w.empty();                  // Should be false
cout << w.get() << endl;  // Prints 8
bool b3 = w.empty();                  // Should be true

w.put(6);
w.put(42);
w.put(-17);
cout << w.get() << endl;  // Prints 6
cout << w.get() << endl;  // Prints 42
w.put(3);
cout << w.get() << endl;  // Prints -17
cout << w.get() << endl;  // Prints 3

Class template WaitInLine should be implemented in header waitinline.h. Since this is a template, there is no associated source file.

What to Do

1. Write class template WaitInLine, in file waitinline.h, as above. The resulting code should compile and pass all tests in test_waitinline.cpp.

Other Stuff

• Get things to compile first!
• Don’t forget “const”.
• Don’t worry about what member function get does if the line is empty. We will leave it up to the caller to ensure that get is never called on an empty line.
• vector has members push_back and pop_back, but there are no corresponding push_front and pop_front for the other end. However, you can do the operation we would want pop_front to do using the following (here, v is a vector).

  [C++]

  v.erase(v.begin());

  Note: This code uses iterators, which we will look at during the next class meeting.

• There is a standard name for a structure that handles data in a first-in-first-out manner, like WaitInLine. It is called a queue (pronounced like the letter “Q”).
• By the way, the above design for class template WaitInLine is flawed; it does not allow for proper error handling. We will discuss this in the next class meeting as well.