Digital Technology 2650 考試技巧

計算機程式

常見錯誤

1. 1high涉及分數: 3Database keys and relationships

   In relational database questions, candidates give a primary key value from one table when the question asks for the foreign key linking it to another table.

   如何避免: Before answering, identify which table the question is asking about. The foreign key sits in the table on the many side of the relationship and repeats the primary key value from the one side.
2. 2medium涉及分數: 2Data validation

   Validation algorithm answers confuse a range check with a presence check, or state a boundary comparison without giving both limits.

   如何避免: Name the check precisely: a presence check confirms data was entered at all, a range check confirms it falls between two stated limits. State both the upper and lower limit when describing a range check.
3. 3medium涉及分數: 4Sorting algorithms

   Bubble sort and insertion sort get described interchangeably, without distinguishing adjacent comparisons and swaps from building a sorted sublist by inserting one item at a time.

   如何避免: Learn the two mechanisms separately. Bubble sort compares neighbouring pairs and swaps them if out of order, repeating passes until no swap is needed. Insertion sort takes each item in turn and inserts it into its correct position in the already sorted part of the list.
4. 4medium涉及分數: 3Encryption

   Encryption is defined vaguely as protecting data with a password rather than as converting plaintext into ciphertext using an algorithm and a key.

   如何避免: Use the precise definition every time: encryption converts readable plaintext into scrambled ciphertext using an algorithm and a key, so that the data is unreadable without the matching key to reverse the process.
5. 5medium涉及分數: 3Loop constructs in algorithms

   Input validation algorithms use a fixed count FOR loop where the question needs a loop that repeats until valid data is entered.

   如何避免: A FOR loop only suits a known, fixed number of repetitions. Validation needs a WHILE or DO WHILE loop that keeps asking for input until a condition, such as the value being within range, is finally met.
6. 6medium涉及分數: 2Array indexing in algorithms

   Array algorithms reference the wrong element because of zero-based versus one-based confusion, for example accessing traffic[2] when the third element is intended.

   如何避免: Write out the index positions on scrap paper before coding the loop. If an array has 5 elements and starts at index 0, the loop condition should stop before index 5, not at index 5.
7. 7high涉及分數: 6QWC extended response

   In 6 mark QWC questions that raise two concepts, such as phishing and denial of service, candidates fully explain one and give only a sentence on the other.

   如何避免: Split your answer space in two before you start writing and give both concepts roughly equal development. An answer that only covers one side is capped below the top band regardless of how detailed that one side is.