Data that stays.

Why use files?

In the lab, choose Write a file, then read it. The program saves three names to Names.txt; the file panel shows the data that would still be there after the program stops.

• Permanent storage: data in a file is kept after the program closes or the computer is switched off.
• Reuse: the data can be read back next time the program runs, e.g. saved settings, a high score or a game save.
• Sharing: one program can write a file that another program reads, or that can be sent to someone else.
• Large amounts of data: data can be loaded from a file instead of typed in every time.

Writing to a file.

Open the file in WRITE mode, write each item with WRITEFILE, then close it. Each WRITEFILE writes one item, a single value or a whole line of text, as a new line.

DECLARE Name : STRING
DECLARE Count : INTEGER
OPENFILE "Names.txt" FOR WRITE
FOR Count ← 1 TO 3
    INPUT Name
    WRITEFILE "Names.txt", Name
NEXT Count
CLOSEFILE "Names.txt"

The same idea in Python (for comparison only: the exam uses pseudocode)

with open("Names.txt", "w") as file:   # "w" = write mode; the file is closed automatically
    for count in range(3):
        name = input()
        file.write(name + "\n")

Reading from a file.

Open the file in READ mode. Each READFILE reads the next line of the file into a variable, starting from the first line.

DECLARE HighScore : INTEGER
DECLARE Score : INTEGER
OPENFILE "HighScore.txt" FOR READ
READFILE "HighScore.txt", HighScore
CLOSEFILE "HighScore.txt"
INPUT Score
IF Score > HighScore
  THEN
    OPENFILE "HighScore.txt" FOR WRITE
    WRITEFILE "HighScore.txt", Score
    CLOSEFILE "HighScore.txt"
    OUTPUT "New high score!"
ENDIF

The syllabus example copies one line of text from one file to another:

DECLARE LineOfText : STRING
OPENFILE "FileA.txt" FOR READ
OPENFILE "FileB.txt" FOR WRITE
READFILE "FileA.txt", LineOfText
WRITEFILE "FileB.txt", LineOfText
CLOSEFILE "FileA.txt"
CLOSEFILE "FileB.txt"

The same idea in Python (for comparison only: the exam uses pseudocode)

with open("HighScore.txt", "r") as file:
    high_score = int(file.readline())