First macro#

A very simple program is often called "Hello World". Here all we are asking the computer to do is print the phrase "Hello World".

Hello world#

Open the ImageJ editor as described previously (Plugins > New > Macro). In this window, type the following:

print("Hello World");

You should see a window titled Log appear with the words Hello World printed in it. Congratulations, you've written your first computer program!

It's worth taking a moment and understanding what is going on here.

First, we've told the computer we would like to do (print something). This is called a function and we will see many more of these as we progress through the course.

Second, we've told the computer what we would like it to print (in this case the string Hello World). This is called an argument and it gives the function a specific piece of information that it needs.

Lastly, we want to tell the computer "OK, we're done giving you instructions, you can go ahead and do what we told you to do". In the ImageJ macro language, we do this by placing the ; symbol at the end of the line. This is very important, and in fact, if you forget to do this, your code will fail.

Ok, but here it doesn't fail? Well, depending on the instructions that you ran, it might not have mattered. But 99% of the errors you will get when writing your macro is going to be because of a missing ; at the end of some line.

Don't Panic!

Don't worry about typing the wrong thing and making an error. The worst case-scenario is that you will have to force your script to stop running. So don't be afraid of trying things and seeing what works (and what doesn't!). An important part of learning to program is learning from your mistakes!

Calculator#

We can also just use this window as a simple calculator. For example, we can type mathematical operations, such as:

print(10 + 3);
print(5 * 6);
print(90 / 9);

This can be very useful -- practice a few yourself.

Of course, we want to do more with our programs than printing out cute messages and using it as a calculator. In the next section we will learn how we can store and manipulate information using variables.