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

Tuesday September 20, 1994

Assigned Reading: 2.4 - 2.5

Handouts (available on-line): none

Topics Covered:

• Expressions. Rules for forming integer expressions. Here's a copy of the operator precedence and associativity table.
• A program that uses expressions in unexpected ways and a sample run.
• The modulo operator, %, can be used to calculate the remainder of an integer divided by another integer. (E.g., 7 % 4 is 3.) We can use the modulo operator to modify the program that converts centimeters to feet and inches. Program and sample run.
• Mixing types can lead to strange results. Generally, if a binary operator is used on both an integer and a double, the integer is converted to a double and the result is a double. So, dividing a 9.0 by 4 gives the double value 2.25. Dividing 9 by 4 gives the integer value 2. Here's a program and sample run that demonstrates division and mixing types.
• Expressions that change the value of one or more variables are said to have a side effect. For example, an expression that uses the assignment operator has a side effect. Since side effects can be unpredictable, expressions with side effects should be avoided. The only exception is simple assignment statements. Here's a program with unpredictable side-effects. The sample runs on different machines give different results. This is because C does not explicitly say if the left subexpression or the right subexpress of a binary operator should be evaluated first.
• Rules for naming variables.
• Discussed shorthand assignment operators: +=, -=, etc. We also discussed the difference between ++x and x++.