lab1

CS2005 - D Term, 2004
Lab 5
April 28, 2004

Purpose

To make progress on Homework 4.

What you should do...

If you have already turned in your completed program

Sign the pregrading sheet and wait your turn to go over your assignment with the TA.

If you have done some work on Homework 4

Sign the attendance sheet.
Continue working on the assignment. Depending upon how much progress you have already made, you may want to incorporate some of the suggestions given below into your program, but it is not necessary to do so. Ask the SAs for help if you get stuck on any part of the assignment.
Before you leave the lab, turn in your client file hw4.cxx. It's OK if it's incomplete, just turn in whatever you have completed at this point. The command you should use to turn in your file is
```
/cs/bin/turnin submit cs2005 hw4 hw4.cxx
```

If you haven't yet started Homework 4

Sign the attendance sheet.
This program will be easier to write if you define subordinate functions to do some of the work for you. If you haven't already created the file hw4.cxx, do that now. Put in the include statements your program will need, the "using namespace std;" statement, and define an empty main function. Now you are ready to write some of the supporting functions.
The first function to put into your program is evaluate_stack_ops(). This should be pretty easy to write, since the code is given in the textbook! (page 351). Type this code into your program, (also type the pre- and post-conditions given on page 349), and add a prototype for the function at the beginning of your program.
Another function that will prove to be useful is eat_spaces(). This function should read and discard any spaces it encounters in the input stream, returning when either the input stream goes bad, or when a non-space character has been reached. eat_spaces() will be very similar to eat_white() (which is given on page 789 in the textbook). Define eat_spaces() as a function in your program, add the pre-and post-conditions, and add a prototype.
A third function you should write is higher_precedence(). This Boolean function takes two arguments, both of which are characters. Each of these characters will be one of the arithmetic operators ('+', '-', '*', '/'), or a left parenthesis ('('). higher_precedence() should return true if the first argument has higher precedence than the second argument, and false otherwise (interpreting the phrase "higher precedence" the way it is normally defined for arithmetic operators). Code the function, write the pre- and post-conditions, and add the prototype.
If you still have time left in the lab period, continue working on the assignment. Here are a couple of other hints to keep in mind as you develop the program:
- Write your program so that it is able to correctly evaluate a single line of input. Once you get the program working correctly for one arithmetic expression, add the loop that handles multiple lines of input.
- Write your program so that it is able to correctly evaluate well-formed arithmetic expressions. Once you get the program working correctly for well-formed expressions, add the code that will be able to detect and print error messages for expressions that are not well-formed.
Before you leave the lab, turn in your client file hw4.cxx. It's OK if it's incomplete, just turn in whatever you have completed at this point. The command you should use to turn in your file is
```
/cs/bin/turnin submit cs2005 hw4 hw4.cxx
```
You have until Monday, May 3 at 11:59pm to finish this homework and turn in the completed files.