File handling and writing a complete program

Last time

Before we start: last time, in Selection and iteration, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Close the program, lose the data?

Everything a program keeps in variables and arrays disappears when it closes. To keep scores, names and settings, a program writes them to a file. The next time it runs, it reads them back. That is file handling, and it is part of the longest question in Paper 2.

Why store data in a file?

A file keeps a permanent copy, so the data is not lost when the program closes. The data can be used again, by this program or another, or moved to another computer.

Five statements

OPENFILE for WRITE creates the file, or replaces its contents. OPENFILE for READ opens an existing file. WRITEFILE writes the value as a new line. READFILE reads the next line into a variable. CLOSEFILE closes it.

The three marks

Open the file in the correct mode, write or read. Read or write the correct variable. Close the file when you have finished. Copy the file name exactly from the question, including dot t x t.

Writing several lines

Open the file for writing. Loop through the array, and write each name on its own line. Close the file. Anything that was in the file before is replaced.

Reading them back

Open the same file for reading. Each READFILE brings in the next line, one name at a time. Close the file. If the file holds Ayesha, Bilal, Chen, Dana and Eli, then position three is Chen.