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Computer Programming for Absolute Beginners

Selection with the if statement

Explore how to use if statements to introduce decision-making in your programs. Understand basic, compound, and nested conditions, including the use of else and elif, to create dynamic control flow and handle multiple potential cases in your code.

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The if statement

Now we know that we have selection and iteration statements and that they work with conditions, so let’s see how we can write code that uses them. Let’s start with the most common selection statement, if.

When using selection in our programs, we could argue that the application uses some sort of intelligence because it can now make decisions and do different things depending on various conditions. So, how can we make our applications smart? Well, the easiest way is with the use of if statements, which are sometimes just referred to as conditions. In most languages, they’ll have a similar structure.

If we write a small program that asks the user for their age, the first part might look something like this:

Python
print "Enter your age: "
input age

Here, the program prints Enter your age: on the screen. The user then enters an age and presses the Enter key to confirm the input. The value entered will be stored in the age variable.

Now, we want to give different feedback depending on the age entered:

Python 3.10.4
if age < 18 then
    print "You are young"
end_if

Here, we have the condition where we check if the age is below 18. If so, we’ll print the message, You are young. The condition is that the age must be below 18. If it’s 18 or above, nothing will happen, because the program will skip everything between them and end the if ...