Trace tables and algorithm dry run

After code has been written, it is vital it undergoes testing. Without testing, there is a chance the code will not work.

Trace tables

When designing , it is common to use a technique known as .

To create a trace table, map out all of the variables which change (not constants) and write them down in a column in a table. Each row will then store what assignments happen as the code is run. Reading through code and noting down values in a trace table is known as a .

Consider the following code to find even numbers between 0 and 3:

1 for i in range (0, 3):
2     if i % 2 == 0:
3         print(i)
4     i += 1

The following Trace Table could be used to dry run the code:

Program Line Number	Value of variable i	Output
1	0	-
2	0	-
3	0	0
4	1	-
1	1	-
2	1	-
3	1	-
4	2	-
1	2	-
2	2	-
3	2	2
4	3	-
1	3	-
2	3	-
3	3	-
3	4	-

Program Line Number	1
Value of variable i	0
Output	-

Program Line Number	2
Value of variable i	0
Output	-

Program Line Number	3
Value of variable i	0
Output	0

Program Line Number	4
Value of variable i	1
Output	-

Program Line Number	1
Value of variable i	1
Output	-

Program Line Number	2
Value of variable i	1
Output	-

Program Line Number	3
Value of variable i	1
Output	-

Program Line Number	4
Value of variable i	2
Output	-

Program Line Number	1
Value of variable i	2
Output	-

Program Line Number	2
Value of variable i	2
Output	-

Program Line Number	3
Value of variable i	2
Output	2

Program Line Number	4
Value of variable i	3
Output	-

Program Line Number	1
Value of variable i	3
Output	-

Program Line Number	2
Value of variable i	3
Output	-

Program Line Number	3
Value of variable i	3
Output	-

Program Line Number	3
Value of variable i	4
Output	-

Next up

Watch a video

��tv

Digital design principles - CCEATrace tables and algorithm dry run