We’ve created many different computer programs by now, but they have all had one thing in common: they only have a single execution path in the program. This means that, each time we run the program, we’ll execute the exact same pieces of code and perform the same operations on each variable. We may have different initial values stored in those variables, but that is really the only difference.

To better visualize this, we can actually think of the execution path of a program just like a flowchart. For example, here is a flowchart showing the execution path of a program that asks the user to input a number and then prints the square of that number.

However, what if we’d like our programs to be able to perform different actions, depending on the user’s input? Wouldn’t that be useful?