Files

Interactive vs. Batch

All of the programs so far have been "interactive":

• data entered through keyboard
• results displayed on screen

In many situations this is not appropriate.

The alternative is "batch" processing, using files:

• no interaction during execution
• data read from file (created earlier)
• results written to file (printed later)

Why use files?

• reduce typing
  • edit (and check) contents once, run program multiple times
  • most valuable with large data sets
• preserve output
  • screen is transient
  • file is permanent
• communicate between programs

Prompt vs. Echo

You should always ensure what the user sees is fully self-explanatory.

You need to do this differently for interactive programs and batch programs.

• interactive programs:
  1. "prompt" to user
  2. read values

          PUT ("Enter hours worked : ");
          GET (hours);
  

• programs using files:
  1. read values
  2. "echo" to output

          GET (hours);
          PUT ("Hours worked = "); PUT (hours);
  

Types of files

Files can be either

• text files: just a stream of characters in text format
• structured files: containing structured data in binary format

Here we focus on text files.