If and Else statements

If and Else statements take a boolean and based on the value will run some code. Basically, its a way to conditionally run some code.

examples of some uses:

Give the user a different greeting if they have a specific name
Only allowing entry to someone over the age of 18
Making a quiz
Moving a player character if a certain key has been pressed

These control flow statements are the crux of programming. They are what really make complex logic possible.

If Statement

An if-statement works by saying “if this condition is true, run this code”.

import stdlib::*;

define main() {
    if 8 == 8 {
        println("eight does in fact equal 8.");
    }
}

The code in the if-statement will only run if 8==8 evaluates to true.

import stdlib::*;

define main() {
    name = "Monty";

    if name == "Monty" {
        println("Is your last name 'Python' by chance?");
    }

    println("I run regardless of the name!");
}

Else Statement

An else-statement must come immediately after an if-statement. This is a block of code that should only be run if the if statement failed.

import stdlib::*;

define main() {
    name = "Monty";

    if name == "Monty" {
        println("Is your last name 'Python' by chance?");
    } else {
        println("You need a cooler name!");
    }

    println("I run regardless of the name!");
}

Chaining else and if

If and Else can be chained to create more complex constructions, that looks like this.

import stdlib::*;

define main() {
    name = "Monty";

    if name == "Monty" {
        println("Is your last name 'Python' by chance?");
    } else if name == "George" {
        println("Is your last name 'Washington' by chance?");
    } else {
        println("You need a cooler name!");
    }

    println("I run regardless of the name!");
}

Note

The whitespace isn’t important! You can also write the above example with extra space.

import stdlib::*;

define main() {
    name = "Monty";

    if name == "Monty" {
        println("Is your last name 'Python' by chance?");
    }

    else

    if name == "George" {
        println("Is your last name 'Washington' by chance?");
    }

    else {
        println("You need a cooler name!");
    }

    println("I run regardless of the name!");
}

Some people might say it looks a little cursed like this, but it’s your code. Just be careful when working on a team to follow their prefered styles.

Multiple Conditions

Sometimes you want to check for multiple conditions. Sometimes you might also want to only run code if a condition is false

We can use these following operations:

cond1 and cond2 - checks if both conditions are true. If one is false, the output is false
cond1 or cond2 - If on condition is true, the output is true, regardless of the other condition.
not cond - Gets the opposite of the boolean. False becomes true and true becomes False.

Here is an example of this being put to use.

import stdlib::*;

define main() {
    name = "Bob";
    age = 22;

    // Try this: See if you can find a way to remove the "not"
    //           and still have it do the same thing.
    if (name == "Bob" or name == "Bill") and not age < 18 {
        println("Great name, and great to know you are an adult!");
    } else if age < 18 {
        println("Adult's only. Get out of here kid!");
    } else {
        println("You need a much better name to get into this club!").
    }
}

Tip

Sometimes you may want to split the condition onto several lines. This can make it easier to read. Just split it at a good location.