Hello World

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👋 Hello world

Let’s start with the traditional first program, Hello World in C3:

import std::io;

fn void main()
{
    io::printn("Hello, World!");
}

The import statement imports other modules, and we want printn which is in std::io.

Next we define a function which starts with the fn keyword followed by the return type. We don’t need to return anything, so return void. The function name main then follows, followed by the function’s parameter list, which is empty.

fn void main() {}

Note

The function named main is a bit special, as it is where the program starts, or the entry point of the program.

For Unix-like OSes there are a few different variants, for example we might declare it as fn void main(String[] args). In that case the parameter “args” contains a slice of strings, of the program’s command line arguments, starting with the name of the program, itself.

🔭 Function scope

{ and } signifies the start and end of the function respectively, we call this the function’s scope. Inside the function scope we have a single function call to printn inside std::io. We use the last part of the path “io” in front of the function to identify what module it belongs to.

📏 Imports can use a shorthand

We could have used the original longer path: std::io::printn if we wanted, but we can shorten it to just the lowest level module like io::printn. This is the convention in C3 and is is known as “path-shortening”, it avoids writing long import paths that can make code harder to read.

std::io::printn("Hello, World!");
io::printn("Hello, World!");

The io::printn function takes a single argument and prints it, followed by a newline, then the function ends and the program terminates.

🔧 Compiling the program

Let’s take the above program and put it in a file called hello_world.c3.

We can then compile it with:

c3c compile hello_world.c3

And run it:

./hello_world

It should print Hello, World! and return back to the command line prompt. If you are on Windows, you will have hello_world.exe instead. Call it in the same way.

🏃 Compiling and running

When we start out it can be useful to compile and then have the compiler start the program immediately. We can do that with compile-run:

$ c3c compile-run hello_world.c3
> Program linked to executable 'hello_world'.
> Launching hello_world...
> Hello, World

Want more options when compiling? Check the c3c compiler build options.

🎉 Successfully working?

Congratulations! You’re now up and running with C3.

❓ Need help?

We’re happy to help on the C3 Discord.