Module Design and Implementation

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a simple example is used to illustrate the design and implementation of modules.
This example is based on a stack of integers

we want a module to produce a stack of integers. There may be multiple instances of these stacks

in this case a module encapsulates a data structure and the functions that are used to manipulate it

the data structure is hidden in the module, it is only visible to the module's functions, other functions can only manipulate it by calling stack module functions

we view the stack module as a state machine, at any point in time each stack is in a particular state. The module's functions are used to move the stack from one valid state to another

how do we design a module? One approach is to list the operations that we would like to perform, this works well with our example

since we can have multiple stacks, we need functions to create and destroy stacks. In addition we will need routines to push and pop from the stack

In addition to this basic functionality, we need a few functions that return the stack's state, functions for testing whether the stack is full or empty, and one for peeking at the top element of the stack

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March 1, 1999

Page 9

C201/TAM