Loops: every key term you need

Loops: Purpose

Repeat code multiple times; reduces duplication. Three types: while, for, enhanced for. Choice depends on situation.

While Loop

while (condition) { statements }. Repeats while condition true. Condition checked before each iteration. Can loop 0+ times.

Do-While Loop

do { statements } while (condition);. Executes body at least once, then checks condition. Rare in practice.

For Loop

for (init; condition; update) { statements }. Typical: for (int i=0; i<n; i++) { }. Combines initialization, condition, update.

Enhanced For Loop

for (type element : collection) { }. Iterates over array/ArrayList without index. Cleaner when order not critical.

Loop Control: break

Exits loop immediately. Used in while loops or when condition complex. Often in switch statements too.

Loop Control: continue

Skips rest of iteration, goes to next. Example: skip negative numbers in processing.

Nested Loops

Loop inside loop; careful with complexity (n² iterations). Example: print multiplication table (rows, columns).

Loop Design Patterns

Accumulator: sum/count values. Sentinel: loop until special value. Flag: check if condition met. Max/min: track largest/smallest.

Infinite Loops

Condition always true; runs forever. Usually mistake but sometimes intentional. Break to exit.

Unit 4 Summary

Loops repeat code. While: condition-based. For: count-based (typically). Enhanced for: iterate collections cleanly.

More AP Computer Science A guides

• Primitives
• Using Objects
• Boolean Expressions
• Writing Classes
• Arrays