- Hello! Welcome to the  Path to Programming; the audio supplementary
  materials for introduction to computer science!
- I am a former student that took this introductory course and today I
  want to talk to you about conditionals!
- Life is filled with making decisions, every moment you weigh the
  options at hand and make a decision based on what will be most useful
  for you at a given moment. If it is sunny outside you take your
  sunglasses, if it is raining outside you take an umbrella with you, if
  you are hungry you eat food etc. Well you’re not the only one that
  makes decisions, so can your computer!
- How does your computer make decisions, and what goes on behind the
  scenes for your computer to make a decision?
- Today we will talk about booleans which help your computer make
  decisions, and conditionals which will actually make them. 

- We talked about different data types in the past weeks like int, float, str (string) and input.
- Bool is another Python data-type!
- A bool can have two values: it can either be True or False.
- These are called Boolean values, named after George Boole, who invented algebraic logic.
- The first letter of each Boolean values must be capitalized when you
  are writing code.
- To be able to get Boolean values you need to be able to compare other
  values. Booleans naturally arise when you compare values, for example,
  if you assert that a variable x is greater than 5, that comparison will
  be either True or False.
- In order to compare values you need to use relational operators.
- There are many relational operators and you should go over each one to
  make sure that you understand the purpose and meaning of each one. Some
  of the relational operators are "greater than," "less than or equals,"
  and "not equals."
- You can use relational operators to compare different types of values.
  For example, just like in math you can use it on floats or integers.
- When you execute the line of code that states “Five is greater than
  six” your computer will give you the Boolean value of False as you
  would expect, just like a mathematical operation that you are used to.

- But relational operators are not limited to numbers, you can also use
  them on strings! This can be done in Python because Python
  automatically assigns a value to each character in a string.
- For example if you execute the line of code that states “bat is less
  than cat” your computer will give you the Boolean value of True. This
  is because b comes before c in the alphabet therefore b is assigned a
  lower number compared to c, and therefore is less than (just like when
  sorting a dictionary, only if the first letters of two strings are tied
  will the second letters factor into the comparison).
- One thing to look out for when comparing string values in differences
  in upper and lower case letters.
- In most programming languages uppercase letters come before lowercase
  letters, meaning lowercase letters have a higher value associated with
  them. So if you executed the line of code that states “uppercase C cat
  is less than lower case b bat” you would get the Boolean value of True
  since lower case b has a higher value (97) than the upper-case C (67). 

- Some other logical operators that you will be using are not, and, or.
  These logical operators work just like they sound in English.
- The not operator evaluates to the opposite of the truth value. For
  example if you executed a line of code that states “not parenthesis
  three is greater than five close-parenthesis“ you would get True
  because three is not greater than five.
- The and, or operations are kind of easy to mix up but the most
  important difference between them is that the "and" operation is used
  when you want to check that ALL of the statements you are making are
  true. When you are using the "or" operation you are checking if AT
  LEAST one of the statements you are making is True.
- For example if you executed a line of code that stated “(Three is less
  than five AND bat is less than cat)” you would get the boolean value of
  True since both statements are true. And if you executed a line of code
  that stated  “(Three is greater than five OR bat is less than cat)” you
  would still get True, even though one of those statements is false, as
  three is not greater than five. But that doesn't matter because the or
  operator checks to see if at least one of the statements made is True.
- Something that really helped me distinguish between using "and" and
  "or" was making Truth Tables.

- A truth table is when you take two expressions and evaluate what the
  resulting boolean value would be based on the different operators you
  are using and the different bools the expressions can have. Making your
  own truth table is a great exercise if you feel stuck trying to figure
  out the differences between "and" and "or."
- Understanding the differences between them is really important because
  as you improve at coding you will start combining logical operators.
  Meaning you will execute lines of code that feature multiple logical
  operators. So you could be executing a line of code that has multiple
  and’s and or’s!
- That’s why it’s really important to know how to keep track of the
  results. In those cases, you should always use parentheses to
  explicitly specify how the operators are grouped with their operands.

- Now that you have the tools to evaluate boolean values by using logical
  operators, let’s get more  into conditionals!
- A conditional is a block of code that starts with the word "if,"
  followed by a condition expression which will evaluate to a Boolean
  value. When you write if, your computer can’t just run the code like it
  normally does, it has to make a decision!
- That’s why using conditionals is very powerful and now that you have
  all the tools to code a conditional let’s get into how you can actually
  code it.
- The first thing your computer does when you execute an if statement is
  to gather all of the lines of code which are indented at the same level
  as the first line of code following the if line.
- This is why indenting is very important, you want to tell your computer
  which lines of code to apply the if statement to, and you do this
  through indentation.
- If you indented correctly the condition expression that you have
  written using relational operators will be simplified and you will get
  a boolean value of either True or False.
- If the boolean value of your conditional expression is True, then the
  lines of code that you had written will be executed, but if it was
  False then that block of code will be skipped over.
- As you can see, using conditionals is very powerful, because you are
  essentially telling your computer to only execute some code when you
  know a condition you want is satisfied. By using conditionals you can
  make your computer essentially make decisions!

- Just to go over what we talked about:
    - There is a new type we learned about called Boolean. A boolean type
      has two possible values, either True or False.
    - These are called boolean values.
    - You can write a conditional by using the keyword "if" and use
      relational operators in your conditional statement, and essentially
      tell your computer which line of codes you want it to execute and
      which ones you want it to skip over.

- The power of if statements is definitely undeniable! But you are not
  just limited to if statements because you can also have else and elif.
- What do else and elif statements do? Let’s say you wrote a block of
  code (indenting multiple lines at the same level) after an if statement
  and then you wrote a new block of code (indented at the same level as
  the if block) putting an else before it, indented to match the if.
- In this situation, if the first block of code with the if statement was
  skipped over because the condition of the if was False, then you are
  guaranteed to execute the else block of code (we call these branches).
- Essentially using an else statement with an if statement guarantees
  that you always execute one branch or the other. Because if the if
  branch isn't executed the else branch always will be. And vice versa,
  if the if branch is executed the else branch will always be skipped
  over.
- This means that the if and else branches are mutually exclusive. This
  quality is what ensures there is always some branch of code that is
  executed no matter whether the if condition evaluates to True or False!

- Besides the else statement there is also an elif statement.
- If/else allows you to create two mutually exclusive branches, but what
  if you need more?
- For example, the outcome of a game might be a win, a loss, or a tie. In
  this case, we might want three different things to happen depending on
  these three possibilities, and we can add an elif branch between our if
  and else branches to achieve this.
- If a block of code after an if statement block of code (indented at the
  same level) starts with elif, the condition on the if block is
  evaluated first, and if it's true, the elif will be skipped, along with
  the else.
    - But if the if condition is False, the elif condition will be
      evaluated, and if it's True, that block will be executed (and the
      else will be skipped).
    - If both the if and elif conditions are false, any further elif
      cases will be checked, and if their conditions are all False, a
      final else block will execute (if it's present).
- Essentially the elif block of code allows you to check multiple
  expressions for True one-by-one, and execute a block of code as soon as
  one of the conditions evaluates to True.
- Elif and else statements are not required when you are writing
  conditional statements, the only required statement is the if
  statement. But they can be very powerful tools, and you will mostly
  likely need to use them.
- Another important note to add is that an elif statement can be used
  multiple times in your code following an if statement, to set up as
  many branches as you need, however there can only be one else statement
  following an if statement!
- If this all seems hard to follow, don’t worry. When you are thinking
  about executing conditionals take each statement one step at a time and
  evaluate whether each statement will be a True or a False and based on
  that move on to the next statement.
- A very helpful visual tool can be making flow charts. You can basically
  draw a diagram of what will happen when each line of code will be
  executed. 


- At a high level, Booleans are Python's way of representing True or
  False, and conditionals are set up using if, elif, and/or else to allow
  Python to use Booleans to make decisions about whether or not to
  execute certain blocks of code.
- To create conditions for conditional statements, we usually use
  comparison operators or custom functions that return Booleans to
  specify the conditions that we want to use.
- Put all of these things together, and your code can be a lot more
  flexible than what's possible just using function definitions alone.
- This was Path to Programming hope! It was great talking to you, see you
  next time.