Lesson 1.4: Inputs, Outputs, and Value Tracing

An input is information a program or operation receives. An output is information it sends out. In the practice runner, blocks provide inputs to other blocks, and the print block sends visible output.

A trace records important values in execution order. It answers questions such as: What was score before this command? Which expression produced the next value? What was printed?

Consider this program:

1. Set score to 4.
2. Print score.
3. Change score by 3.
4. Print score.

Its outputs are 4 and 7. The first print does not change when a later command changes the variable.

Guided practice

Build that program, predict both outputs, and use Step to verify the trace. Then set bonus to 2 and change score by the value stored in bonus.

Make a small table with one row per instruction. Include the instruction number, score, bonus, and any new output. If the actual trace differs from your table, find the first row that differs before editing the program.

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