Categories: All Variables and Constants  String manipulation  Builtin functions  Input and output  Arrays  Conditional logic  Repetition / Iteration  Functions / Procedures 

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This resource is designed as a quick revision guide and must not be used by students during a NEA where internet access is not allowed. It has not been endorsed by any exam boards. If you spot any mistakes, please let me know and I'll fix them asap.

Introduction

This website aims to give a quick reference for VB.NET, Python and pseudocode and is aimed primarily at teachers & students working towards a GCSE in Computer Science

VB.NET and Python are both programming languages designed to be understood and followed by computers. Pseudocode is not a programming language: it's written to be understood by humans so that they can turn it into any programming language.

Each exam board has published a document saying how they'll write pseudocode in their exams. The whole idea of syntax (a set of rules) for pseudocode is silly - it's not designed to be a programming language that is run by a computer. With this in mind, all exam boards state that you don't have to follow the syntax for 'their' version of pseudocode when you write out your own algorithms, but you should be able to understand their version of pseudocode when reading an algorithm in an exam.

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For loop
   

A for loop is a count-controlled loop which means it your code says exactly how many times the loop should repeat. 

A for loop will use a variable to count between the minimum and maximum value. This variable is called the index, which is why for loops often use the variable i.

A for loop is an example of definite iteration because the number of times the loop repeats is clearly defined.

This example will count from 10 to 20

FOR i FROM 10 TO 20 DO SEND i TO DISPLAY END FOR
For i = 10 To 20 MsgBox(i) Next i
for i in range(10,21): print(i)
for i = 10 to 20 print(i) next i
for i = 10 to 20 output i next i
For loop (with step)
   

for loop is a count-controlled loop which means it your code says exactly how many times the loop should repeat. 

A for loop will use a variable to count between the minimum and maximum value. This variable is called the index, which is why for loops often use the variable i.

Rather than increasing the index by 1 each time, you can step up by any amount until you reach the maximum.

This example will count down from 10 to 1 then say "Blast off!" 

FOR i FROM 10 TO 1 STEP -1 DO SEND i TO DISPLAY END FOR SEND "Blast off!"
For i = 10 To 1 Step -1 MsgBox(i) Next i MsgBox("Blast off!")
for i in range(10,0,-1): print(i) print("Blast off!")
// There isn't a for loop with step specified // but the following while loop does the same thing i = 10 while i >= 0 print(i) i = i - 1 endwhile print("Blast off!")
{ There isn't a for loop with step specified } { but the following while loop does the same thing } i is integer set i = 10 while i >= 0 output i set i = i - 1 repeat output "Blast off!"
For Each loop
   

A for each loop means the code in the loop will run once for each item in an array.

This means it is a count-controlled loop because the number of times the loop will run is not dependent on a condition being met: you know how many times it will repeat in advance.

A for each loop is an example of definite iteration because the number of times the loop repeats is clearly defined.

This example will display the lyrics for "The wheels on the ... go round and round"  for an array containing the strings "bus", "car" and "tram"

SET vehicles TO ["bus", "car", "tram"] FOR EACH vehicle FROM vehicles DO SEND "The wheels on the " & vehicle & " go round and round" TO DISPLAY SEND "Round and round, round and round" TO DISPLAY SEND "The wheels on the " & vehicle & " go round and round" TO DISPLAY SEND "All day long" END FOREACH
Dim vehicles As String() vehicles = {"bus", "car", "tram"} For Each vehicle As String In vehicles Msgbox("The wheels on the " & vehicle & " go round and round") MsgBox("Round and round, round and round") MsgBox("The wheels on the " & vehicle & " go round and round") Msgbox("All day long") Next For
vehicles = ["bus", "car", "tram"] for vehicle in vehicles: print("The wheels on the " + vehicle + " go round and round") print("Round and round, round and round") print("The wheels on the " + vehicle + " go round and round") print("All day long")
// there's no for each loop specified // but the following code does the same thing array vehicles vehicles[0] = "bus" vehicles[1] = "car" vehicles[2] = "tram" for i = 0 to 2 vehicle = vehicles[i] print("The wheels on the " + vehicle + " go round and round") print("Round and round, round and round") print("The wheels on the " + vehicle + " go round and round") print("All day long") next i
{ there's no for each loop specified } { but the following code does the same thing } vehicles[3] set vehicles[0] = "bus" set vehicles[1] = "car" set vehicles[2] = "tram" for i = 0 to 2 set vehicle = vehicles[i] output "The wheels on the " + vehicle + " go round and round" output "Round and round, round and round" output "The wheels on the " + vehicle + " go round and round" output "All day long" next i

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