CS 111: Introduction to Computer Science

Getting started, with a focus on strings

The lab exercises

Each of these programs contains instructions for you. To get started, save a copy of each of the files listed below in your working directory, open each file in turn, and follow the instructions, trying to answer the questions posed there. You do not need to hand in any of your answers. However, you should try hard to understand how each of the programs works, line by line. Ask questions during lab, during prefect sessions, in my office hours, or in class.

• strings0.py -- getting started
• strings1.py -- slicing
• strings2.py -- string methods
• strings3.py -- formatted strings
• strings4.py -- iteration over strings

There are lots of ways to explore sample programs like these, but here's a recommended procedure. For each sample program:

• Download the program to your working directory by right-clicking on the link and choosing "Save Link As" or whatever similar option your browser gives you.
• Open the sample program in a text editor (TextWrangler is a good choice).
• Read the program with your partner. Discuss what you think the program will do.
• Run the program (by typing, for example, "python strings0.py" in the Terminal window. See if your predictions about the program were true. If not, try to figure out why not.
• Try to answer the questions in the program's comments. You may want to test your answers by making changes to the program in your text editor, saving the changes, and running the program again. Play around with the program until you feel comfortable with all its operations.
• Move on to the next program.

Your assignment, due 11:59PM Wednesday

Write a Python program that asks the user for a string, and then prints out the following items, one item per line:

• The user's string, but all upper case.
• The user's string, but with all spaces removed.
• The user's string, but with each space replaced by a pound sign (#).
• The first half of the user's string. (It the string has an odd number of characters, then print the smaller half. For example, for an 11-character string, print 5 characters.)
• The number of letters in the user's string (see the "isalpha()" operation at http://docs.python.org/library/stdtypes.html#id4 for a handy tool.
• The user's string, but backwards.

Your program should begin with a comment like the ones in my sample programs that includes the name(s) of the student(s) who wrote the program. If you work with a partner, you only need to submit one copy of the program.

Submit this program by 11:59PM on Wednesday, April 8. Submit your program either by dragging it to the hand-in folder for this course, or by using the Homework Submission Program (HSP). HSP is generally pretty convenient if you are working on one of the 3rd-floor CMC lab computers. If you're on your own computer connected to ResNet, it's probably a lot easier to drag your work to hand-in.

Start early, have fun, and keep in touch.