Now that we know the basics of print statements, variables, and reading in input from the user – we can combine all these awesome skills with conditional statements. Conditional statements allow the computer to make decisions based off the value of an expression. In the real world, we use conditional statements all the time to make decisions! For example, if it is raining outside, then I use an umbrella. In this example, the I evaluated the weather outside and because it was raining, I made the sequential decision to use an umbrella.
What conditional statements can you think of that you use in everyday life?
We’ll start off with an if statement in its simplest form! Looking at the real world example, you can see certain words used and those apply to programming statements as well. If it is raining outside, then I use an umbrella.
if tells us that we need to make a decision. Then we have the decision to make. Is it raining? That question is called the expression. Then, if it is raining, I use an umbrella. That is a statement that applies when the expression is truthful.
if (expr): statement
Shown above we have three different parts:
- If – this tells the computer that we are going to be deciding based off the expression inside the parenthesis
- Expr – this represents the expression that we are evaluating. If the expression is “truthful” then the computer will enter the if statement and execute the statement.
- Statement – what the computer will complete if the expression is “truthful”
x = 0 y = 5 if (x<y): #truthful print('yes') if (y<x): #falsy print('yes') if (x == 10): #falsy print('yes')
Let’s break down the example above and decide why some statements are “truthful” or “falsy”.
We are given two variables
y are they are each assigned a value. In the first if statement we are testing if the value of
x is less than the value of
0 is less than
5, this is true! So, the first
if- statement will print yes.
However, we can see that
y is not less than
x, so it evaluates to
false. The inside of the
if statement will not be executed then. The same applies for the
if statement evaluating if
x is equal to
10. We see that
x is equal to
0, so this expression is
false, and the inside of the
if statement won’t be executed.
Now that we know how to use if statements to conditionally execute a single statement or multiple statements, let’s see what
else we can do!
Sometimes, you need to evaluate a condition in order to act accordingly if it is
true, but if it
false we act differently. Here is the simplest form of the
if (expr): statement1 else: statement2
This is really like the
if statement! However here, if the
if statement is
false (not truthful), the program will automatically execute the
statement2 in the
A real-life example is if I’m hungry, I’ll eat. Else (in other words, I’m not hungry), I won’t eat. Let’s take a look in python code!
if (hungry): eat else: dont_eat
Let’s put together everything we’ve learned so far! Let’s see if we can create a program that prompts the user for their name. The user can write their name into the console. Then the computer can decide if their name is equal to your name and print out a response. Else, print out a different response!
Hint: Try talking out the different paths a computer can take! Make sure to identify what the if and else conditions are.