Abstraction

Abstraction is the concept of taking a step back from something, and providing a wider overview.

It does NOT mean to be vague, but rather give a higher level of meaning.

Example
If we swap two variables with swap(&var1, &var2),
the user doesn’t need to know about the temp variable that is needed.

How to implement this, abstraction thing..?

There are two parts to an ADT, the interface, and the implementation

When designing a library,
What are the abstract properties of the datatypes we want to provide?

Interface

An ADT’s interface is the components that are exposed to the user to see and use. These are usually placed in an ADT’s file header (.h file).

Example
Function prototypes: void swap((void*)var1, (void*)var2)
Structure pointers: typedef struct st *St

Fun Fact: The C language allows us to forward-declare function and types - We term these as prototypes

Implementation

An ADT’s implementation is the actual inner-workings of the ADT… Helper functions, variable states, etcetera

Uses of Abstract Data Types

Stacks and Queues are common types of ADT implementations.

Stacks (LIFO)

The Last In is the First Out

Interface

The interfaces would be the functions that a program would use

  • Stack stack_new(item_t)
  • void stack_push(Stack, item_t)
  • item_t stack_pop(Stack)
  • size_t stack_size(Stack)
  • item_t stack_peek(Stack)

Implementation

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Stack stack_new(item_t item) {
  ... malloc ...
  ... assign ... // (*stack) = (struct stack) { ... }
  ... return ...
}
void stack_push(Stack s, Item it) {
  ... add item to tail of stack ...
}

Queues (FIFO)

The First In is the First Out

Interface

  • push
  • pop
  • size
  • peek

Implementation

code for queue functions go here!!

Analysis and Testing

It’s important to test our code… to make sure that it works.
> It’s also important to check for the efficiency of our code… more on that in the next lecture.

Approaches

TDD - Test Driven Development

Write tests for your code with expected values BEFORE you write your code.

(Often people write their code, then test it against output values… this isn’t writing tests, as all of your tests will be false negatives)

Unit Tests

Testing each function

Integration Tests

Testing functions together

Regression Tests

Testing that further development has not affected previous behaviour

Read more about testing on StackOverflow

Black Box / White Box Tests

There’s also another two types of testing.

Black Box Tests as aptly named - you don’t know what’s inside the black-box, only the inputs and outputs. For these tests, we compared the output given an input.

White Box Tests on the other hand, is testing with knowledge of the inner workings of the code. Here we’d be checking for structure values, counters, pointer locations, etcetera.

The lecturer wrote some stuff about Black and White Box Tests