Dry Run Testing & Trace Tables

Learning Objectives


You have just completed a piece of code but when you run it, it does not behave as expected.

One way to check and troubleshoot your code is to perform a dry run using a trace table.

Trace tables are used by programmers to track the values of variables as they change throughout the program. This is useful when a program is not producing the desired result.

Context / Starter activity


A primary teacher likes to start her maths lesson by displaying a number sequence maths challenge on the board. Here are the last three challenges she has used with her class. Can you solve these?

Number Sequence #1:number-sequence-2
Number Sequence #2:number-sequence-3Number Sequence #3:number-sequence-1

The primary teacher decided to create some Python script to help them create similar number sequences.

Here is the pseudo-code for her first script:

number = 3
PRINT number
FOR  i  from 1 to 3:
      number = number + 5
      PRINT number
PRINT "?"

To make sure her script is working she decided to complete a dry run test using a trace table. See animation below:
trace-table-s

View the complete trace table.

Challenge #1


Step 1: Complete the trace table for the following script:

number = 5
PRINT number
FOR  i  from 1 to 3:
      number = number + i
      PRINT number
PRINT "?"

Step 2: Implement this code using a high level programming language (e.g. Python) and compare your trace table with your actual output of your program.

Challenge #2


Step 1: Complete the trace table for the following script:

number1 = 2
number2 = 5
PRINT number1
PRINT number2
FOR  i  from 1 to 4:
      number1 = number1 + number2
      PRINT number1
      number2 = number1
PRINT "?"

Step 2: Implement this code using a high level programming language (e.g. Python) and compare your trace table with your actual output of your program.

Challenge #3


Think of your own number sequences. Write the pseudo-code, the trace table and implement them using a high level programming language (e.g. Python).

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