Add Comments to Programs

When you write code, it is a good practice to add comments that describe the code. Comments allow others to understand your code and can refresh your memory when you return to it later. During program development and testing, you also can use comments to comment out any code that does not need to run.

In the Live Editor, you can insert lines of text before and after code to describe a process or code. Text lines provide additional flexibility such as standard formatting options, and the insertion of images, hyperlinks, and equations. For more information, see Create Live Scripts in the Live Editor.

Note

When you have a MATLAB® code file (.m) containing text that has characters in a different encoding than that of your platform, when you save or publish your file, MATLAB displays those characters as garbled text. Live scripts and functions (.mlx) support storing and displaying characters across all locales.

To add comments to MATLAB code, use the percent (%) symbol. Comment lines can appear anywhere in a program file, and you can append comments to the end of a line of code.

For example:

% Add up all the vector elements.
y = sum(x)           % Use the sum function.

To comment out multiple lines of code, use the block comment operators, %{ and %}. The %{ and %} operators must appear alone on the lines that immediately precede and follow the block of help text. Do not include any other text on these lines.

For example:

a = magic(3);
%{
sum(a)
diag(a)
sum(diag(a))
%}
sum(diag(fliplr(a)))

To comment out a selection, select the lines of code, go to the Editor or Live Editor tab, and press the button. You also can type Ctrl+R. To uncomment the selected lines code, press the button or type Ctrl+T.

To comment out part of a statement that spans multiple lines, use an ellipsis (...) instead of a percent sign. For example:

header = ['Last Name, ',      ...
          'First Name, ',     ...
      ... 'Middle Initial, ', ...
          'Title']

The MATLAB Editor includes tools and context menu items to help you add, remove, or change the format of comments for MATLAB, Java®, and C/C++ code. For example, suppose that you have this lengthy text into a commented line.

% This is a program that has a comment that is a little more than 75 columns wide.
disp('Hello, world')
With the cursor on the line, go to Editor tab and in the Edit section, press the button. The Editor wraps the comment:
% This is a program that has a comment that is a little more than 75
% columns wide.
disp('Hello, world')

The button is not available in the Live Editor or in MATLAB Online™.

By default, as you type comments in the Editor, the text wraps when it reaches a column width of 75. To change the column where the comment text wraps or to disable automatic comment wrapping, go to the Home tab and in the Environment section, click Preferences. Select MATLAB > Editor/Debugger > Language, and adjust the Comment formatting preferences.

The Editor does not wrap comments with:

  • Code section titles (comments that begin with %%)

  • Long contiguous text, such as URLs

  • Bulleted list items (text that begins with * or #) onto the preceding line

Changing the comment formatting preferences is not supported in MATLAB Online.

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