Programming and Data Types

Variables

The same guidelines that apply to MATLAB variables at the command line also apply to variables in M-files:

• You do not need to type or declare variables used in M-files, (with the possible exception of designating them as global or persistent).
• Before assigning one variable to another, you must be sure that the variable on the right-hand side of the assignment has a value.
• Any operation that assigns a value to a variable creates the variable, if needed, or overwrites its current value, if it already exists.

Naming Variables

MATLAB variable names must begin with a letter, which may be followed by any combination of letters, digits, and underscores. MATLAB distinguishes between uppercase and lowercase characters, so A and a are not the same variable.

Although variable names can be of any length, MATLAB uses only the first N characters of the name, (where N is the number returned by the function namelengthmax), and ignores the rest. Hence, it is important to make each variable name unique in the first N characters to enable MATLAB to distinguish variables.

• N = namelengthmax
  N =
      63
  

Verifying a Variable Name

You can use the isvarname function to make sure a name is valid before you use it. isvarname returns 1 if the name is valid, and 0 otherwise.

• isvarname 8th_column
  ans =
       0                    % Not valid - begins with a number
  

Avoid Using Function Names for Variables

When naming a variable, make sure you are not using a name that is already used as a function name. If you define a variable with a function name, you won't be able to call that function until you either clear the variable from memory, or invoke the function using builtin.

For example, if you enter the following command, you will not be able to use the MATLAB disp function until you clear the variable with clear disp.

• disp = 50;
  

To test whether a proposed variable name is already used as a function name, type

• which -all <name>
  

Private Functions

Local Variables