Getting Started with C

If you’re looking to write programs that are more than simple test apps or demos and are willing to try something a bit more involved, we recommend following the Using Docker to Cross-Compile tutorial instead of this one.

This tutorial walks you through writing a simple C program, compiling it on your ev3dev device, and running it. We will assume that you have already configured a means of connecting to your device from a PC.

Note that C is not a particularly friendly language, especially for beginners. It would be recommended to use Python or another easier language.

For this tutorial, we will be using a text editor called nano. You can refer to our nano cheat sheet for information on nano.

Before you start, make sure that you have configured a network connection to your ev3dev device and have opened an SSH connection to it.

Background on C

To understand what you will be doing in this tutorial, you’ll first need to understand the way that C programs are run. C is a “compiled” language; that means that the code that you write must be converted into a different kind of code that a computer understands before it can run. This is the job of the compiler. The compiler is a program that takes your C code and converts it into something that can be run. If you are familiar with Windows, the final product is the equivalent of a .exe file.

On ev3dev, you will need to run the compiler over SSH to create the executable file. Once you have the binary file, you can run it whenever you want from the terminal or Brickman.

Installing prerequisites

We need to install the compiler and some other tools. Execute the following command to install them:

sudo apt-get update
sudo apt-get install build-essential

Create a project folder

We need a place to store the code that you’ll write. In the terminal, run the following commands:

mkdir c-demo
cd c-demo

Creating a “Hello world” program

The code that you write will live in its own file. Let’s reate a file called main.c and open it in nano:

nano main.c

Now paste the following code into the file (in many cases, you can paste by right-clicking on the terminal window):

#include <stdio.h>
int main()
{
    printf("Hello world!\n");
    return 0;
}

Save the file by pressing Ctrl+O and exit the editor with Ctrl+X.

Creating a “makefile”

A makefile is a file that gives instructions on how your program should be compiled. Makefiles can be very simple (as ours will be here) but it can get more complicated if you have additional C source files or need to include other libraries.

Create a file called Makefile and open it:

nano Makefile

Copy the following contents into the file:

all: main.o
	gcc main.o -o bin
main.o: main.c
	gcc -I . -c main.c
clean:
	rm -rf *.o
	rm bin

When you paste the contents into nano, the indentation will likely disappear. Move your cursor using the arrow keys to the beginning of the lines that are indented above and press Tab to indent them.

Running the compiler

Now we’re ready to use the makefile to compile your code. Run the command make. If it is successful, the output should look like this:

gcc -I . -c main.c
gcc main.o -o bin

Now type ls and hit Enter. If the compilation did what it was supposed to do, you should see an item called bin.

Executing the compiled program

You can run your new file by typing ./bin in the SSH terminal. You should see the text Hello world! printed back. Congratulations! You have written your first C program on ev3dev.

Making changes

To make changes to your code, you can open the main.c file in nano and edit it. You must then go through the “Running the compiler” step again.

To test your skills, try changing the text in the code to print something other than “Hello world!”

Final notes

If you want to use the motors, sensors, etc. of the EV3, you will need to either use an existing C library (not C++) or manually read from and write to the files that let you control devices. You can find a list of the known libraries on our programming languages page.

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