Class 19: Control Flow: Conditionals (1)

Held: Wednesday, 23 February 2011

Summary: We gain some additional practice with the basic conditional statement in C. We also explore binary search, since K&R introduce it in this section.

Related Pages:

• EBoard.
• Lab: Conditionals in C.
• Reading: K&R 3.1-3.3.
• Due: Assignment 4: Fun with Bits, Bytes, and Beyond.

Notes:

• Happy 1/3rd day!
• The soda supply has been restored.
• I've posted answers to your first questions on conditionals.
• We'll cover questions on Assignment 4 after the preliminaries.
• Tonight's reading: K&R 3.4.
• I hear that some of you are stressed that we're moving a bit fast. We can talk about that a bit.
• EC for tomorrow's CS extra.
• EC for Friday's CS table. (Sorry, I'm behind in printing out readings.)

Overview:

• Basics of C's if statements.
• Binary search.
• Lab.

Basics

• You know the basics:

  if (TEST)
    TRUE-PART;
  else
    FALSE-PART;
  

• Distinguished from conditionals in Scheme in that the two parts are statements, rather than expressions.
  • You can't use the result of a conditional statement.
• The else part is important, since
  • It saves work ... we don't have to recheck the previous test
  • It makes it easier to write a final default statement.
• Best learned through practice.
• C also provides a conditional expression and another form of conditional, both of which we'll cover in the next class.

Binary Search

• There were some questions on K&R's binary search implementation.
• We'll go over it a bit in class.
• What's the basic principle of binary search?
• How do we typically implement that idea in code? (Scheme, C, whatever.)
• Let's wrap the function in something that lets us play with it.
• You can find the code in Examples/KR3/binsearch.c

Lab

• Do the lab
• Be prepared to discuss your solutions.