L8A Variables, Loops & Arrays

Variables

Values that can be changed over time. 

Think about a pointer system, where the variable points to the allocated memory where the value is stored

Assignment Statements

Expression is evaluated first before being assigned to the variable

Conversely, its a variable pointing to a value

Assignment: Pros & Cons

• Allows us to create object with state that can differ over time

• Harder to debug/verify correctness and the subsitution model fails

Assignment vs Declaration

• Assigning a new value to a declared name

• Declaring a new name in a frame, in source names must be declared with a value assigned to it

Why subsitution model breaks down?

The subsitution model fails to account for the changes that happens during the assignment of variables.

In the example, the assignment on line 3 is not reflected in the subsitution model.

Mutable Data

Data that can be changed after being declared.

Arrays (Python Lists)

Data structure that stores a sequence of data elements accessible via index, starting 0. Read and write at Log(1) while in length of array.

Factorial with Loops Example

Break VS Continue

• Break stops the whole loop

• Continue skips the remaining iteration of the loop and moves on to the next iteration

Destructive Function

Function that changes a pair in anyway