Array Memory Allocation

What this lesson covers

• Tell apart an array's length, how many values count, from its capacity, how many boxes are allocated.
• Trace a fixed-capacity append one state at a time: check for room, write at the old length, then move the length.
• State the invariant that elements occupy exactly the indices zero to length minus one, and the two rules it gives.
• Explain why an index reaches its box in constant time, and what a full array costs.
• Spot the common bugs: capacity as the last index, stale values as elements, and writing without a check.

Sections

1. Two numbers that describe an array: Roadmap, then array, index, capacity and length from zero.
2. One example on the board: Put one array on the board and read it carefully.
3. The append, one move at a time: Check for room, write, then move the length.
4. What must stay true: The invariant, the two rules it gives, and how an index finds its box.
5. The algorithm and why it is correct: Turn the three moves into steps, run them, and prove both cases.
6. What the append costs: Count the work, then see what a full array needs.
7. Where implementations break: Three common bugs, each shown wrong, then corrected, plus the edge cases.
8. Putting it together: Walk back through the roadmap and the method for a new problem.

More Arrays & Memory Layout lessons

• Array Reversal and Rotation
• Indexing and Traversal
• Insertion & Deletion in Arrays
• Prefix and Suffix Techniques
• Sliding Window Basics

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