Handout 4

Overview

• Questions from last time
• Control structure practice
• Input-Output (continued)

Control structure practice

• Last time we wrote a little program to print out all the words entered on the command-line with spaces between each word. There were several ways to do this, but here's the simplest one.
• Hong pointed out that this actually puts spaces after every word. First, let's see that this is true by printing something at the end of the sentence. Here's a revision of the first program that does this (example).
• How would we get rid of that last space? There are several ways to do this; here's one (example).

Input-Output

• Prompt. We've already treated prompt output: the print command. Prompt input is straightforward and requires two notions: handles and the IO operator < >. The handle STDIN represents "standard input", what I'm calling the prompt. To read a line from the prompt, you simply use the value returned by <STDIN> (example).
• File. File input and output uses the same basic ideas, but is a little more complex. File input involes first creating a handle from the filename with the open command, then reading from it, and finally closing the handle with close (example).