Lesson Objective
- Understand the purpose of pseudocode.
- Be able to write some simple algorithms using it.
KS3, GCSE, A-Level Computing Resources
Pseudocode is a kind of structured English for describing algorithms.
It allows the designer to focus on the logic of the algorithm without being distracted by the syntax of the programming language.
There are three basic ways of controlling the order in which program statements are carried out.
The statements are executed in the order they are written.
mealCost = 4.00
drinkCost = 2.00
total = mealCost + drinkcost
An IF statement is a selection statement. The next statement to be executed depends on whether the condition being tested is true or false.
hoursPerNight = USERINPUT
IF (hoursPerNight < 8) THEN
  OUTPUT "That's not enough!"
ELSE
  OUTPUT "That's plenty!"
ENDIF
Iteration means repetition. There are three types of iteration statement in most, but not all, imperative programming languages such as Pascal, Visual Basic or Python.
FOR Loop
Use this when you want to execute the loop a specific number of times.
total = 0
FOR counter = 1 TO 7
  maxTemperature = USERINPUT
  add maxTemperature to total
ENDFOR
averageWeeksTemp = Total / 7
OUTPUT "This week's average is ", averageWeeksTemp
WHILE Loop
Use this when you want to execute the loop WHILE a certain condition is true.
emailAddress = USERINPUT
WHILE emailAddress does not contain "@"
  OUTPUT "Invalid address – please re-enter"
  emailAddress = USERINPUT
ENDWHILE
OUTPUT "Thank you"
REPEAT UNTIL Loop
The condition is not tested until the end of the loop (it is always executed at least once), so you need an IF statement as well as the Repeat loop.
OUTPUT "Please enter email address"
REPEAT
  emailAddress = USERINPUT
  IF emailAddress does not contain "@" THEN
    OUTPUT "Invalid address – please re-enter
  ENDIF
UNTIL emailAddress contains "@"
Note: Examples linked to previous Flowchart Lesson.
OUTPUT "Enter User ID" ID = INPUT WHILE ID NOT IN Database THEN OUTPUT "Enter VALID User ID" ID = INPUT END WHILE ADD ID to Database
total = 0 count = 0 count = count + 1 total = total + count WHILE count != 1000 THEN count = count + 1 total = total + count END WHILE OUTPUT total