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📓 Using a C# REPL

We're finally ready to craft our first C# code!

This lesson will explore a tool called a REPL that will allow us to run C# code directly in the command line. This is similar to how we ran JavaScript code using the browser DevTools console in the Intro to Programming and Intermediate JS courses.

The rest of this pre-work section will focus on learning and practice C# basics: data types, variables, methods, classes, type checking, branching, operators, looping, and more! As we'll see, a lot of the concepts we learned in JavaScript will also exist in C#, just with slightly different syntax.

The REPL​

The next few lessons will use a command line tool called a REPL. This stands for READ - EVALUATE - PRINT - LOOP. It works as follows:

  1. We type in a line of code and hit enter. The REPL reads this code.
  2. The REPL then evaluates the code, figuring out what it does.
  3. Next it prints the result of running this code.
  4. Finally, it loops back to step 1 so we can enter more code.

Since we've installed dotnet-script, we have a C# REPL available right in the terminal!

Accessing the REPL​

We can launch the REPL by opening our Terminal application (on a Mac machine) or our GitBash application (on Windows), entering the following command, then hitting Enter:

$ dotnet-script

Regardless of operating system, we should be met with the following:

>

We're now in the REPL! The > symbol is the command prompt for dotnet-script, and this is where we'll enter in all of our commands.

Command Notation​

Before we run code, notice how the command prompt for dotnet-script starts with the > symbol. A command prompt is just that, a symbol that denotes where we can enter in commands. The > is different from the standard terminal command prompt, which looks like this:

Guest-User@Desktop epicodus_student $

Yours will differ slightly, depending on what OS you are on, what your computer's user name is:

Again, notice the REPL precedes the command prompt with > instead of $ or %, like this:

>

When our curriculum depicts commands meant to be run in the REPL, we'll precede them with > instead of $ or %. When you see this, you are not required to type a >. You will only type the command listed after the >.

If you see a command preceded with a $ or %, like you did in Intro and Intermediate JS, that means the command is meant for the standard terminal.

Exiting the REPL​

We can exit at any point by pressing Ctrl + C.

Now that we understand the basics of the C# REPL, let's practice. In the next few lessons, we'll cover how to use strings, variables, numbers and methods with C#.