IGCSE Computer Science 0478 — 8.3 File Handling Hangman

The 19 key terms

1file

A file keeps data on storage so it still exists after the program closes, unlike variables. The program can read it back next time it runs, such as a saved high score or a list of names.

2"FileA.txt"

A file identifier is the name of the file, written as a string in double quotes with its extension, such as "FileA.txt". The same identifier is used in every file command.

3file mode

States what a program will do with an open file: READ gets data out of it, WRITE puts data into it. A file is open in only one mode at a time, chosen by what the program needs.

4DECLARE LineOfText : STRING

Creates a variable named LineOfText that holds text. Declare it before the file commands that use it, for example before READFILE stores a line in it.

5OPENFILE "Scores.txt" FOR WRITE

Opens the file Scores.txt in write mode so data can be written into it with WRITEFILE. The file must be opened before writing. Keywords are in capitals.

7WRITEFILE "Scores.txt", Score

Writes the value stored in a variable into an open file. Give the file name, a comma, then the variable. The file must already be open in WRITE mode.

8WRITEFILE "Names.txt", LineOfText

Writes the text held in the STRING variable LineOfText into the file Names.txt as one new line. Each WRITEFILE adds one more line to the file.

9CLOSEFILE "Scores.txt"

Closes the file named in the identifier once you have finished reading or writing, so data is saved and the file is released. The name must match the one used in OPENFILE.

10CLOSEFILE

Closes an open file so its data is safely saved and the file can be opened again in a different mode, such as READ after WRITE. Use one CLOSEFILE for each OPENFILE.

11OPENFILE "Scores.txt" FOR READ

Opens the existing file Scores.txt in READ mode so the program can read data from it with READFILE. The file must already exist, and READ mode does not change its contents.

12READFILE "Scores.txt", Score

Reads one data item from the open file and stores it in the variable. The file must already be open in READ mode, and the variable's data type must match the item.

13READFILE "Names.txt", LineOfText

Reads the next line of text from the open file Names.txt into the STRING variable LineOfText. Each READFILE call reads the following line. Declare the variable first.

15FOR Index ← 1 TO 30

A count-controlled loop. It repeats the indented statements once for each value of Index, from 1 up to 30, going up by 1 each time. NEXT Index closes the loop.

16FOR Count ← 1 TO 5

A FOR loop with INPUT and WRITEFILE inside repeats a fixed number of times, writing one item to the open file on each repeat. CLOSEFILE goes after NEXT.

18WRITE, CLOSEFILE, READ

Open a file for WRITE, store data with WRITEFILE, then CLOSEFILE. Reopen the same file name for READ and READFILE gets the data back to use again.

19WRITEFILE FileB.txt, LineOfText

Writes the line held in LineOfText (read earlier from FileA.txt) into FileB.txt, copying it between files. Both files must be opened first and each one closed after.

20trace table

A table that follows a program step by step, recording the file contents and each variable's value after every file command, until you find the final OUTPUT.

21file handling error

A mistake such as using the wrong mode, missing OPENFILE or CLOSEFILE, using different file names, or opening a file FOR WRITE and wiping its old data.

22DECLARE, OPENFILE, WRITEFILE, CLOSEFILE

The order of a complete file program: declare variables, open the file in the right mode, read or write the data, then close the file. Keywords are in capitals and statements are indented.