Boxes for Values

Imagine a shelf of labelled boxes. Box score holds 0. Box lives holds 3. When the program says score becomes score plus 1, you open the score box, add one, put the new number back.

Each box holds one value at a time. Putting a new value in replaces the old one. The label stays the same.

Watch the compare animation. See clear names versus vague single letters.

total equals price times count uses whatever is inside price and count right now. If price changes later, old totals do not auto-update until you run the line again.

Tracing tables list box names across the top and show each line updating them. That is the next topic.

Try on paper: lives starts at 3, then lives becomes lives minus 1 twice. What is left?

Before syntax in a language, you need the picture: boxes, labels, replacement. Every language copies that idea.

Open the trace table lab soon and watch boxes change row by row.

Good names are a kindness to future you when homework is due next week.