SYLLABUS 8.3 · PAPER 2 · ALSO FOR 0984 AND 2210

File handling: OPENFILE, READFILE and WRITEFILE

Variables are lost when a program ends. Storing data in a file keeps it, so it can be used the next time the program runs, or by a different program.

Why use files

Data is stored permanently, so it isn’t lost when the program closes.
The data can be read again later, or by another program.
Large amounts of data don’t have to be typed in every time.

Writing and reading

A file is opened in a mode: WRITE to create it (replacing anything already in it) or READ to take data from it. WRITEFILE puts a line into the file, READFILE takes the next line into a variable, and CLOSEFILE closes it when you’ve finished.

DECLARE Title : STRING
OUTPUT "Enter a song title"
INPUT Title
OPENFILE "Songs.txt" FOR WRITE
WRITEFILE "Songs.txt", Title
CLOSEFILE "Songs.txt"

OPENFILE "Songs.txt" FOR READ
READFILE "Songs.txt", Title
CLOSEFILE "Songs.txt"
OUTPUT "Saved:", Title

Where marks go

Forgetting to open the file, or opening it in the wrong mode.
Not closing the file afterwards.
Opening for WRITE when the old contents should be kept, since WRITE replaces them.
Leaving out the file name in READFILE or WRITEFILE.
Saying files are used “to save data” without saying the data is kept after the program closes.

Try a question

3 MARKS · MARKED ON THIS PAGE

A music app saves the title of the song a user has just added so it is not lost. Write a program in pseudocode that: - declares the variables Title and SavedTitle as STRING - inputs a song title into Title - opens the file "playlist.txt" for writing, writes Title to the file and closes the file - opens "playlist.txt" again for reading, reads the line from the file into SavedTitle and closes the file - outputs the message Saved: followed by SavedTitle, using OUTPUT "Saved: ", SavedTitle Do not output any other messages or prompts.

solutionPseudocode

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