Idea 8of 23Builds onA loop can make a pattern
Trace code in a table
How do you keep track of a number that changes many times?
Today you'll discover
- how to set up a trace table
- how to fill one row per line
- how to read the output from it
Think firstSET 10, then REPEAT 3 TIMES: MULTIPLY BY 2, SUBTRACT 3
What is the number after the first pass of the loop?
Decide first, then press Next. Fill one row for every line that runs, in order.
Code: SET 10, REPEAT 3 TIMES with MULTIPLY BY 2 and SUBTRACT 3 inside, END, OUTPUT. A trace table with columns for the pass, the line that runs and the number: 10; pass 1, 10 to 20, 20 to 17; pass 2, 17 to 34, 34 to 31; pass 3, 31 to 62, 62 to 59; OUTPUT 59. The last step asks for the number after pass 2 of SET 2 with ADD 4 and MULTIPLY BY 2 inside.
See the whole ideathe big idea and the key word, in one place
The big idea
A trace table writes down every line as it runs, with the number after it.
The first rowsSET 10 gives 10. Pass 1: MULTIPLY BY 2 gives 20, then SUBTRACT 3 gives 17. Pass 2 starts from 17.
Easy to get wrongFinish every line of the loop body before you start the next pass. Pass 1 ends after SUBTRACT 3, not after MULTIPLY BY 2.
Key word
- trace table
- a table with one row for each line of code as it runs, and the number after that line
Ready to use it?
- Fill in a trace table for a loop.
- Find the number after any pass.