Determining the purpose of simple algorithms

When given an , there are a number of ways to determine what the purpose of the algorithm is. Sometimes it is clear as the algorithm is simple; however, at other times it is useful to ‘dry run’ the algorithm to see what is taking place.

Dry running an algorithm means to assign the values to of an algorithm and to do any processing that takes place without translating it into code.

Trace tables

enable the variable values in an algorithm to be recorded as the algorithm is dry run. For example, using the times table algorithm below, a table could be created showing the value of the variables num and number as the program runs:

num ← USERINPUT
FOR number ← 1 TO 10
  OUTPUT number * num
ENDFOR

Num	Number	Output
1	5	5
2		10
3		15
4		20
5		25
6		30
7		35
8		40
9		45
10		50

Num	1
Number	5
Output	5

Num	2
Number
Output	10

Num	3
Number
Output	15

Num	4
Number
Output	20

Num	5
Number
Output	25

Num	6
Number
Output	30

Num	7
Number
Output	35

Num	8
Number
Output	40

Num	9
Number
Output	45

Num	10
Number
Output	50

Visual inspection

Some algorithms follow a pattern that can be recognised. Many of these are referred to as and often follow a set pattern for searching for or sorting . Sometimes it is clear what this is just by looking at the . For example, the algorithm below follows a recognisable pattern for searching through each letter of a word and checking if the letter entered matches. This would be a useful decomposed part of a hangman game.

guess ← USERINPUT
FOR i ← 0 TO LEN(word)
   IF word[i] = guess THEN
     OUTPUT “found”
     ENDIF
ENDFOR

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Fundamentals of algorithms - AQADetermining the purpose of simple algorithms