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Unit 4: Iteration

5 dot points across 5 inquiry questions. Click any dot point for a focused answer with worked past exam questions where available.

How do you traverse a String with a loop to count, search or transform its characters?

Topic 4.3 Developing Algorithms Using Strings: traverse a String with a loop using length, substring and indexOf to implement standard algorithms such as counting characters, searching for a pattern and building a new String.
A focused answer to AP CSA Topic 4.3, covering String traversal with a for loop, extracting one character with substring, the standard counting, searching and accumulation patterns, the half-open index range, and bounds safety, with a fully worked example.
11 min answer →

How does a for loop package initialisation, condition and update into one header, and when do you use it?

Topic 4.2 for Loops: use a for loop, whose header combines initialisation, a boolean condition and an update, to repeat a block a controlled number of times, and convert between for and while loops.
A focused answer to AP CSA Topic 4.2, covering for-loop header syntax (init; condition; update), the order in which the three parts run, counting iterations, equivalence with while loops, common patterns, and tracing, with a fully worked example.
11 min answer →

How do you count how many times a statement executes in a loop, including nested loops?

Topic 4.5 Informal Code Analysis: determine the number of times a statement executes in a loop or nested loop by counting iterations, without using formal big-O notation.
A focused answer to AP CSA Topic 4.5, covering how to count statement executions in single and nested loops, the effect of step size and start/end bounds, conditional statements inside loops, and triangular versus rectangular counts, with a fully worked counting example.
10 min answer →

How do nested loops work, and how do you count the total iterations of an inner loop inside an outer loop?

Topic 4.4 Nested Iteration: write and trace nested loops, where an inner loop runs in full on each pass of an outer loop, and count the total number of inner-loop iterations.
A focused answer to AP CSA Topic 4.4, covering nested loops, how the inner loop completes fully on each outer pass, counting total iterations (including triangular patterns where the inner bound depends on the outer variable), and tracing nested output, with a fully worked example.
11 min answer →

How does a while loop repeat a block of code, and how do you avoid an infinite loop?

Topic 4.1 while Loops: use a while loop to repeat a block of statements while a boolean condition remains true, with correct initialisation, condition and update to avoid infinite or off-by-one loops.
A focused answer to AP CSA Topic 4.1, covering while loop syntax, the initialise/test/update pattern, why each loop control variable must change, infinite loops and off-by-one errors, and how to trace iterations, with a fully worked example.
11 min answer →