UMBC CMSC201, Computer Science I, Fall 1994 Sections 0101, 0102 and Honors

Tuesday September 27, 1994

Assigned Reading: 3.4 - 3.6

Handouts (available on-line): none

Topics Covered:

• Cleared up some confusion about Project 1. Comments on Project 1 are posted on WWW.
• Anonymous mail and practice quizzes on WWW should be working again.
• More loop examples: A program that adds the digits of a number that the user types in and sample run.
• A more robust version of the same program that checks the user's input is positive. Program and sample run.
• "99 Bottles of Beer on the Wall". A program that demonstrates that you should not test floating point numbers for equality. The culprit is that 1/5 is not a terminating fractional number in base 2 (similar to 1/3 in base 10). Program and sample run.
• A note on how to represent fractions in base 2.
• A discussion on how to get formatted output using printf. (E.g., how to left justify, or print out only a certain number of digits after the decimal point.) Examples for floating point numbers, strings, and integers (last one was not shown in class).
• Some simple programs using an if statement.
  Testing an input integer to check if it is even or odd: Program and sample run. Testing an input integer to check if it is positive, negative or zero: Program and sample run.
• Programs which show the "dangling else". Where there are two if's and only one else, the else is matched with the closest if.
  First program and sample run.
  Second program and sample run.
• A very common bug is using one = instead of == to test for equality in an if statement. A seemingly correct program can produce strange results.
  Program and sample run.
• Using Boolean variables and operators.
  Program and sample run.