Program Architecture

• Which procedures will be written?
• How will they communicate?
• How will they be assembled to produce the final program?

Designing procedures

Top down decomposition

• procedures represent sub-tasks
• hierarchy of actions
• partition by function
• high levels manage, low levels do the work

Bottom-up programming

• procedures for low-level operations first
• high-level (managing) code later

Examples

• TEXT_IO : procedures for character & string I/O
• Screen I/O: draw window, move to location, ...

    clear_screen;
    move_to ( row => 10, col => 20);

• Input repeatedly, until value within a given range

    get_integer (num, 1, 10);
    get_integer (val, 0, 100);

Benefits: incremental development, re-use

Alternative architectures

The same basic structure can be implemented in several different ways.

For example, even a trivial program which just reads in and then adds two integers might be structured in the following ways (among others).