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Variables, Operators and Conditionals

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Recap From Last Lecture

  • Computer programming is how we tell computers what to do
  • The computer language we will cover in this class is python
  • We will be using Google Colab in this course
  • https://colab.research.google.com/drive/1zIqXLcrAUxfoJzSvCQbBfVZWxd-Q2Oln?usp=sharing

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Upcoming Schedule

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Today's Agenda

  • Variables and Data Types
  • Arithmetic Operators
  • Logical and Relational Operators
  • Concept of Branching
  • If/Else Statements
  • Case Switch Statements

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Variables and Naming Conventions

  • A variable is a name that refers to a value stored in computer memory.

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  • In programming, there exist two standard naming conventions for variables. Snake case and Camel case.
  • Snake case means separating words using an underscore (e.g. my_name)
  • Camel case means separating words using capital letters for the first letter of each word except the first (e.g. myName)

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Data Types and the Assignment Operator

  • In Python, variables have four primitive data types: Integer (int), Floating Point (float), String (str) and Boolean (bool).
  • You do not have to explicitly specify the data type as the compiler infers it using the value you assign
  • You can “type cast” between data types in Python using the built-in int(), float(), bool() and str() constructors, only where it makes sense.

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The “=” used here is called the assignment operator and as its name explains, is used to assign values to variables

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Arithmetic Operators

  • Arithmetic operators are used to perform mathematical operations on data.
  • In Python, there are 7 arithmetic operators:

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  • Arithmetic operators can also be used in conjunction with the assignment operator to make code shorter.
  • For example, “a = a + b” can be rewritten as “a += b”

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Logical and Relational Operators

  • Boolean Algebra is the branch of mathematics that deals with operations on logical values with binary (true or false) values
  • We are interested in using concepts from boolean algebra in our code
  • Why? How?

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Why?

→ To keep track of T/F values within a program

→ Booleans take up very little memory

→ To create conditions that can control how a program acts in certain settings

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How?

We can utilize logical operators like:

  •     “and” returns true if both statements are true       
    • x < 5 and x < 10
  •     “or” returns true if one of the statement is true   
    • x < 5 or x < 4
  •  “not” returns false if the result is true or false
    • not(x < 5 and x < 10)

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 We can also use == (equal), != (not equal), > (greater than), < (less than), >= (greater than or equal to), <= (less than or equal to). These are known as relational operators.

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Exercise: Branching

Could there be certain times when a program must act one way if something is true, and another way if not?

Think of one real-world example of a program that would require this

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If Statements

If statements may have two more branches, only one of which is executed at a time.

The “if” branch is executed if the condition, and the “else” branch is executed if the condition is false.

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If Statements continued

To address this we use “elif” (stands for else if)

For example, a program that sorts items into two boxes that needs to act differently when sorting odd, even, and an empty collection of objects.

Are there examples of a program needing to check more than one conditional in some process?

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Individual Exercises