Introduction into Macro Programming

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Why Macros?

Macros can be used to

  • automate repetitive tasks
  • document what you did
  • share common procedures
  • add tools to the toolbar
  • add keyboard shortcuts

Variables

The most important concept when starting to program macros are variables. A variable is a placeholder for a changing entity. It has a name and a value, which can be numeric or text (so-called strings).

Variables are needed whenever you want to execute the same code several times, but for different images, parameters, etc

Variables can also be used to store user input obtained through a dialog.

A variable can be assigned like this:

factor = 1024;

In this example, factor is the name of the variable, 1024 is the value assigned to the variable. The semicolon tells ImageJ that the assignment is done.

Example: assign text to a variable:

message = "Hello, World!";

In this case, the variable is named message, and the text Hello, World! is assigned to it; Text is specified inside double quotes.

Using variables

You can use variables in expressions: you can calculate with numeric variables, and you can concatenate text and text variables. Example:

x = 2;
y = 3;
result = x * x + y + y;

This assigns the variable x the value 2, the variable y the value 3, and then assigns the variable result the square of x plus the square of y.

This example shows how to concatenate a fixed text with the value of a variable:

name = "Bob";
msg = "Those days are over, " + name;