Unit 4 Cycle 1 Day 8: Counting Matches
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Counting Matches
Section 4.3 — Common Array Algorithms
Key Concept
Counting matches traverses an array and increments a counter each time an element satisfies a condition. The pattern is: initialize count = 0, loop through the array, and if (condition) count++. The condition can be any boolean expression involving the element: equality, range, divisibility, or string properties. On the AP exam, counting questions may involve complex conditions or counting elements that match a relationship with other elements (e.g., elements greater than their predecessor).
Consider the following code segment.
What is printed?
Answer: (A) 2
Grades >= 90: 92 and 95. Count = 2.
Why Not the Others?
(B) 88 is less than 90, so it is not counted.
(C) Only 2 of the 6 grades meet the threshold.
(D) 6 is the total number of elements, not the count of those >= 90.
Common Mistake
The counting pattern: initialize counter to 0, increment when condition is met. This is one of the most common array algorithms on the AP exam.
AP Exam Tip
Counting pattern: int count = 0; for each element: if (condition) count++;. Make sure the condition matches exactly what is asked.