Code tracer
Step through real exam-style code one line at a time and watch every variable change. This is the skill behind most of the multiple-choice section — every trace below was recorded by actually running the program, so what you see is exactly what happens.
while loop with integer division
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.
Nested loops where the inner bound depends on the outer
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.
Enhanced for loop does not modify the array
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.
Removing from an ArrayList in a forward loop (the bug)
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.
Binary search — tracking low, high, mid
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.
Recursion — factorial, calls and returns
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.
Counting substring occurrences
Step through with the buttons, or use the ← → keys. Changed variables are highlighted.