Outline of Class 10: Control Structures

Miscellaneous

• As some of you know, I'm setting up a small multimedia laboratory. I'd appreciate feedback on equipment. You can find a rough draft of the equipment list at http://www.math.grin.edu/~rebelsky/Glimmer/proposed_equipment.html.
• I still haven't graded the first homework (sorry, but I can't grade from home, and William keeps me at home on weekends), but I'll try to get it graded by Wednesday.
• We can spend part of today discussing the homework assignment.
• Just a reminder that I won't have office hours tomorrow.

Control Structures

• As do most imperative languages, Java provides a number of control structures for manipulating program flow, including if statements, switch statements, for loops, and while loops.

Basic Conditionals

• Java provides the two basic forms of the if statement.
• if (test) statement executes the statement only when the test holds.
  • Note that the test must return a boolean value.
  • Note that the test must be surrounded by parentheses.
• if (test) statement else statement selects between the two statements. It executes the first if the test evaluates to true and the second if it evalutes to false.
• Java does not provide a special facility for nesting if statements.

The Block Statement

• In many places in your programs, you will want to include more than one statement, but only one statement is allowed.
• What can you do? It might be possible to create a separate function to handle the multiple statements, but this seems wasteful.
• Java permits you to create a block of statements by surrounding them with curly braces, as in

  {
    statement1;
    statement2;
    ...
    statementn;
  }
  

The Switch Statements

• Often, you need to do more than select between two values, one true and one false.
• While it is possible to do this with a sequence of if statements, such a solution is neither readable nor efficient.
• As an alternative, Java provides the switch statement (like the case statement in Pascal).
• It takes the form

  switch (integer-valued-expression) {
    case value1:
      stuff-to-do;
      break;
    case value2:
      stuff-to-do;
      break;
    ...
    default:
      stuff-to-do;
      break;
  }
  

• If you leave out a break, execution will continue into the next case.
• You can switch on byte, short, int, long, or char valued expressions.
• break has other uses, which you'll see later.