10.3 Thinking Procedurally

Breaking a problem into a number of sub-problems, so that each sub-problem accomplishes an identifiable task (sub-problems may be divided even more)

A method of writing a computer program which uses: - Modularization for program structure and organisation (breaking the problem down into subroutines) - Structured code for the individual modules - that is, code which uses the basic constructs of sequence, selection and iteration - Recursion

To show overall program structure

• Each logical process is broken down into smaller components until it cannot be broken down any further • Execution takes place from left to right, always at the lowest level component • Selection and iteration are not shown in a hierarchy chart

• Large programs are broken down into subtasks/subroutine that are easier to program and manage • Each subroutine can be individually tested • Modules can be re-used several time in a program • Frequently used modules can be saved in a library and used by other programs • Several programmers can simultaneously work on different modules, shortening development time • Easier to find errors in small self contained modules • Well-organised, modular program is easier to follow • Easier to find which module needs to be changed • Self-contained modules mean that the change should not affect the rest of the program • New features can be added by adding new modules

• Programs are more easily and quickly written • Programs are more reliable and have fewer errors • Programs take less time to test and debug • Programs are easier to maintain

• Meaningful indentifiers • Define and document the inputs, outputs and preconditions for each sub-procedure • Add lots of meaningful comments within the program • At the bottom level, each sub-procedure should perform a single task • Keep each sub-procedure self-contained by passing parameters and using local variables

Involves writing procedures or functions and passing parameters