AP CSP Day 58: Procedures & Parameters | Cycle 2
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Higher-order procedure design involves writing a general procedure that accepts another procedure or a condition as a parameter, enabling flexible reuse across different scenarios. On the AP CSP exam, this concept appears when a procedure is designed to apply different operations to a list depending on a parameter value. Cycle 2 procedure review questions ask students to complete or correct a general-purpose procedure so it works correctly for multiple described use cases. Recognizing which part of the algorithm should be fixed (the procedure body, the parameter list, or the calling code) is the key diagnostic skill.
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General-Purpose Procedures: Design and Debugging
What Makes a Procedure General-Purpose?
A general-purpose procedure performs a task that is useful across multiple different contexts by parameterizing the parts that vary. Instead of writing separate procedures for each case, one well-designed procedure with the right parameters handles all cases.
Debugging Multi-Use Procedures
When a procedure works correctly in some call contexts but not others, the bug is usually in handling a specific combination of parameter values. Test the procedure with the failing call specifically, trace its execution with those arguments, and compare to the expected result.
Practice Question
What is displayed after the following code runs?
PROCEDURE process(list, threshold)
{
count ← 0
FOR EACH item IN list
{
IF item ≥ threshold
{
count ← count + 1
}
}
RETURN count
}
data ← [15, 22, 8, 30, 12, 25]
high ← process(data, 20)
low ← process(data, 10)
DISPLAY(high)
DISPLAY(low)First call process(data, 20): elements ≥20 are 22, 30, 25 → count=3. Second call process(data, 10): elements ≥10 are 15, 22, 30, 12, 25 → count=5 (only 8 is excluded). high=3, low=5.
B) Five elements are ≥10, not four (12 ≥ 10 is true). C) Three elements are ≥20, not two. D) Not all six elements are ≥10 because 8 < 10.
Students often miss boundary values. For threshold=10, the element 12 satisfies 12 ≥ 10. For threshold=20, the element 22 satisfies 22 ≥ 20. Carefully check each element against the threshold.
When a procedure is called multiple times with different arguments, trace each call independently. Do not carry state from one call to the next — local variables reset with each call.
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