CS 117 Labs, Fall 2000

September 13, 2000

• hello.cpp
• arithmetic.cpp
• decisions.cpp
• loops1.cpp
• loops2.cpp
• cppstrings.cpp
• printwords.cpp

This process of "get the file and follow the instructions and try to answer the questions" is how we will do things on the three or four occasions we have class in lab. I usually try to have plenty of stuff for everyone to do during a 70 minute period, so you may not be able to get through everything during class. If you haven't finished all the lab exercises, come back and finish them up later. The material in these labs is important, so the exercises will stay accessible on the Web all term.

September 25, 2000

• graphics0.cpp
• graphics1.cpp
• graphics2.cpp
• graphics3.cpp

October 4, 2000

I. The ddd debugger

Today, you'll use ddd to (1) watch a variable, (2) single-step through a program, and (3) set breakpoints. All three of these operations should become clear shortly.

1. To use ddd in the first place, you first have to do a weird thing. Use gEdit to open a file called .cshrc.linux that you will find in your account. Don't change anything that is already there, but add the following line to the end of the file:

   setenv LD_LIBRARY_PATH "/usr/local/lib:/usr/lib"

   Save and then close the file. Finally, close any terminal windows you have open and open a new one. You should be ready to go.

2. Save the program odds.cpp in your account, and compile it using the usual command: g++ -g -Wall -o odds odds.cpp

3. Run the command

   ddd odds

4. Open the data display. Select Data Window from the View menu. A grid should appear at the top of the ddd window.

5. Setting a breakpoint. Click in the source code part of the ddd window at the beginning of the line where N is declared. Then click on the "Breakpoint" button. A small stop sign should appear in the source code.

6. Running the program. Click "Run" in the little palette window. The program will run until your breakpoint and stop there.

7. Watching a variable. Double-click on N. A small window with N's name and value will appear in the Data grid. Move it to a convenient spot. You can watch sum, too.

8. Single stepping. The single-stepping feature of ddd allows you to watch how your variables evolve while the program executes one instruction at a time. Click on the "Step" button in the palette. Keep doing so until you step into the SumOfOdds function. Once you're there, double-click on N, odd, and sum to watch those three variables evolve. Keep stepping.

II. Compiler error scavenger hunt

Start with one of the programs you have written, one of the lab exercise programs listed above, or one of the example programs from class. Introduce a small error into it. Remove a semi-colon, add an extra brace (try { one time, } the next), delete a return statement, or whatever. Try to compile the program. Write down the error you introduced, and the first error message the compiler generated. We'll make a master list on the white board.

Be creative. There are lots of ways to confuse a compiler with a tiny mistake.