Class 26: Weakest Preconditions

Held: Tuesday, 4 March 2003

Summary: Today we consider weakest preconditions, a tool for describing the meaning of statements.

Related Pages:

• EBoard.

Due

• Gries 7-8.

Assignments:

• Read K&R on files.

Notes:

• I'll be gone on Friday the 7th for the Pew conference on attracting and retaining majors. Mr. Gum will cover class.
• No class on Friday the 14th.
• Are there questions on homework 5?
• I plan to distribute exam 1 tomorrow. It will be due the 14th.
• One of my CSC153 students had an interesting problem today that we'll look at for a little while. Go to http://www.cs.grinnell.edu/~rebelsky/Courses/CS153/2003S/Examples/dicegame.cgi for the example. (You can find the underlying Scheme code by substituting ss for cgi.)
• We're going to try a different class format today. You'll get to be at the front of the room. You can ask questions of your colleagues and you can also just lecture. I'll have you pass the responsibility regularly.

Overview:

• Preconditions, defined.
• Weakness and strength.
• Using weakest preconditions.