There are only three necessary control structures needed to write programs: sequence, selection, and iteration.

Sequence refers to the line-by-line execution as used in your programs so far. The program enters the sequence, does each step, and exits the sequence. This allows for sequences to do only a limited job during each execution.

Selection is the control structure that allows choice among different paths. Java provides different levels of selection:

• One-way selection with an if structure
• Two-way selection with an if-else structure
• Multiple selection with a switch structure

Iteration refers to looping. Java provides three loop structures. These will be discussed in length in Student Lesson A12.

• while loops
• do-while loops
• for loops