Data types and structures

Cambrdige AS level computer science 2025. Textbook references: Cambridge International AS and A level computer science coursebook Sylvia Langfield, David Duddell 2019 press ||| Cambrdige International AS and A Levels Computer science by David Wastson, Helen Williams press 2019

why are data types important

helps the computer and the user understand the information

what data type is for numbers

integer

what data type is for one letter or one symbol

char

what data type is for mainly words

string

what data type is for decimal

real

what data type is for yes and no or true and false

Boolean

what data type is for a specific date

date

what data type would you for your name

string

what data type would you use for the number of children in a class

integer

what data type would you use for the time taken to run a race

date/time

what data type would you use for whether a door is opened or closed

boolean

what data type would you use for your birthday

date

what is a record

composite date type comprising several related items

what is a random file

file that stores records at specific addresses that can be accessed directly

what is a binary file

where we store records serially or sequentially

what do we use files for

store and read lines of text

what do text files allow you to write

strings in serial or sequential manner

where can you append strings to a file

at the end of the file

what does this do(pseudocode): OPENFILE <filename> FOR WRITE

create a file and open it for writing

what does this do(pseudocode):OPENFILE <filename> FOR APPEND

open a file in append mode

what does this do(pseudocode): OPENFILE <filename> for read

open a file for reading

what does this do(pseudocode): OPENFILE <filename> FOR RANDOM

open a file for random acces

what does this do(pseudocode): CLOSEFILE <filename>

close a file

what does this do(pseudocode): PUTRECORD <filename>, <identifier>

write a record to a file

what does this do(pseudocode): GETRECORD <filename>, <identifier>

read a record from a file

what does this do(pseudocode): SEEK <filename>, <address>

move to a specific disk address within the file

what does this do(pseudocode): EOF(<filename>)

test for end of file

What is going on here?

Dim fileNum As Integer = FreeFile()
FileOpen(fileNum, "filename.txt", OpenMode.Output)

create a file and open for writing

What is going on here?

Dim fileNum As Integer = FreeFile()
FileOpen(fileNum, "filename.txt", OpenMode.Append) 
PrintLine(fileNum, "New data")

opening a file in append mode

What is going on here?

Dim fileNum As Integer = FreeFile()
FileOpen(fileNum, "filename.txt", OpenMode.Input)
Dim line As String
Do While Not EOF(fileNum)
    line = LineInput(fileNum) 
    Console.WriteLine(line) 
Loop

opening a file for reading

What is going on here?

Dim fileNum As Integer = FreeFile()
Dim recordLength As Integer = Len(New Student())
FileOpen(fileNum, "students.dat", OpenMode.Random, , , recordLength)

opening a file for random access

What is going on here?

FileClose(fileNum) 

closing a file

What is going on here?

Dim student As Student
student.Name = "Alice"
student.ID = 101
FilePut(fileNum, student, recordNumber)

writing a record to a file

What is going on here?

Dim student As Student
FileGet(fileNum, student, recordNumber) 
Console.WriteLine($"Name: {student.Name}, ID: {student.ID}")

reading a record from a file

What is going on here?

Seek(fileNum, address)

moving to a specific position (random access)

What is going on here?

If EOF(fileNum) Then
    Console.WriteLine("End of file reached.")
End If

testing for the end of a file

what does lineinput(filenum) do

reads one line

what is append mode

opening a file so that new data is added to the end of the existing content in the file

what is sequential file processing

a way of saving records on a disk before the program quits in order so you don’t lose the data

uses for append mode

saving user input over multiple sessions

what kind of array does random-access file processing use

fixed-length records

why does random-access file processing use fixed-length records

allows computer to directly calculate the position of any record in the file

what does random-access file processing do

store each record in a binary file as the record is created

what can a hashing function calculate

address from the record key and store the record at the calculated address

what does READ do in file handling

read data from the file

what does WRITE do in file handling

writes data to the file

what is the disadvantage of using WRITE when you opened a file

overwrites the data

what is a positive when using APPEND when opening a file

does not overwrite the data

what does APPEND do in file handling

adds data to the end of the file i

is a 1D array a list or table

list

is a 2D array a list or table

table

what is flowchart symbol?

flowline

what is flowchart symbol?

terminal

what is flowchart symbol?

process

what is flowchart symbol?

decision

what is flowchart symbol?

input/output

what is flowchart symbol?

annotations

what is flowchart symbol?

predefined process

what is flowchart symbol?

on-page connector

what is flowchart symbol?

off-page connector

what is flowchart symbol?

delay

what is flowchart symbol?

alternate process

what is flowchart symbol?

data

what is flowchart symbol?

document

what is flowchart symbol?

multi-document

what is flowchart symbol?

preparation

what is flowchart symbol?

display

what is flowchart symbol?

manual input

what is flowchart symbol?

manual operation

what is a flowchart

shapes linked together to represent the sequential steps of an algorithm

what is a flowline for

shows the process’ direction. connects two blocks

what is a terminal symbol for

indicates beginning or end of a flowchart

what is a process symbol for

represent a step

what is a decision symbol for

shows a step that decides the next step in a process. Commonly yes/no or true/false

what is an input/output symbol for

inputting and outputting external data

what is annotation symbol for

indicates additional information regarding a step in a process