This page covers the basic (built-in) datatypes available in Matlab, together with some notes on how they can be used, how they can be converted, and how they relate to one another.

Variables in Matlab have the following general properties:

• variables are accessible via an identifier that must begin with a letter, may contain numbers and underscores, but no symbols or blanks:

  % some valid variable names with assignments:
  v = 1;
  VAR12 = 12;
  A_Really_Long_Name = 'long name';

• please note that if a variable is given the same name as an existing function, the identifier then only refers to the variable (see also precedence rules):

  % defining a new array
  newarray = [1, 2, 3, 4];
   
  % computing the sum
  sumarray = sum(newarray);
   
  % redefining sum
  sum = 5;
   
  % then this leads to an error...
  notthesum = sum(newarray); % index exceeds dimensions!!

• variables can be defined (created) at any time and do not require a declaration (such as in C/C++); this unfortunately makes it sometimes difficult to find out what an identifier stands for (function or variable? what datatype and content?)
• variables can change type and size at any time in the code (although this is bad coding practice and should be avoided):

  % define x as a number
  x = 1;
   
  % re-define x as a string: no error!
  x = 'string';

• access (availability) of variables is organized in workspaces (different function code files can use the same variable names without conflict)
• each variable type supports multidimensional size (older versions would allow up to 63 dimensions, but this limit no longer exists)
• that means that a variable containing a single number is of the same type as a variable containing several numbers (of the same type)
• to access a sub-portion of an array, an index expression has to be provided within parentheses (e.g. part = fullarray(portion);)
• this sub-portion access also works when only a part of an array is to be replaced with new data (e.g. fullarray(portion) = newvalues;)
• in that case, newvalues must either be a single number (all indices addressed by portion will be set to the same number) or must match in size
• if the variable is smaller than indicated by the index expression, Matlab will attempt to grow the variable accordingly:

  % define a 2x3 array
  a = [10, 20, 30; 40, 50, 60];
   
  % assign the value 100 to the second through 4th row and the 3rd through 4th column
  a(2:4, 3:4) = 100;
   
  % a is now a 4x4 array!

By default, a variable in Matlab that is storing a numeric value (or a list/array of numbers) has the datatype “double”. So, in a simple assignment of a number (or array) to a variable (such as a = 1; or b = [2, 3, 4];), the datatype would be double, regardless of whether the number is integer or not! While this requires more memory (for large arrays of numbers), at least the user (or code writer) doesn't have to worry about datatype conversions, etc. Unless you have very specific needs (e.g. lower memory usage or increased speed for specific operations), it is recommended to use the default datatype.

Numeric variables are defined by simply assigning the output of a function that returns a number to a variable or by setting the value(s) manually.

Here is a list of all “numeric” datatypes:

• double (default type for all numbers, supports decimal numbers/fractions): each value being stored requires 8 byte (= 64 bits) of memory, 1 bit for the sign, 11 bits for the exponent, and 52 bits for a base-2 fraction (see Double precision floating point format at wikipedia). Special “configurations” are used to store the values Inf, -Inf, and NaN.
• single: each value being stored requires 4 byte (= 32 bits) of memory; in short, the datatype has similar properties compared to double, just less “precision” (and exponent range)
• int64: a 64-bit (8-byte) integer datatype (signed); lowest value is -2^63, highest value is 2^63 - 1
• uint64: a 64-bit (8-byte) integer datatype (unsigned); lowest value 0, highest value is 2^64 - 1
• int32: a 32-bit (4-byte) integer datatype (signed); lowest value is -2^31, highest value is 2^31 - 1
• uint32: a 32-bit (4-byte) integer datatype (unsigned); lowest value is 0, highest value is 2^32 - 1
• int16: a 16-bit (2-byte) integer datatype (signed); lowest value is -32768, highest value is 32767
• uint16: a 16-bit (2-byte) integer datatype (unsigned); lowest value is 0, highest value is 65535
• int8: an 8-bit (1-byte) integer datatype (signed); lowest value is -128, highest value is 127
• uint8: an 8-bit (1-byte) integer datatype (signed); lowest value is -128, highest value is 127

A special case is the logical datatype. It can only store two values: false or true. If converted to any of the other numeric datatypes, false is converted to 0 and true is converted to 1.

Given that Matlab variables can be arrays of arbitrary size, single characters, as well as “strings” (a series of characters, such as in a word or sentence) and also lists of strings (two-dimensional field of characters) all are stored with the same basic datatype: char.

Here are some examples defining variables of type char:

letter = 'x';
start = 'The letter is';
sentence = [start, ' ', letter, '.'];

The resulting variable then contains the string “The letter is x.”.

Importantly, the underlying storage is yet a numeric datatype:

% the difference between to characters
'd' - 'a'
 
% is their distance in the alphabet, in this case 3!

In many situations it is necessary to store data of different types (e.g. a name/string together with a number, such as age) in a “dataset”, which still should be accessible via a single variable. For this purpose, Matlab provides the cell datatype.

To define a cell array as well as to address the content of a cell, Matlab uses the “curly braces” characters: { and }:

% define a 1x2 cell array with a name and an age
name_and_age = {'John Doe', 41};
 
% to access just the name we index the first cell with {1}
name = name_and_age{1};
 
% and for the age the second cell
age = name_and_age{2};

Please be aware that a cell array can, naturally, also be indexed with the parentheses syntax. However, in that case the returned value will be of type cell. In fact, every index expression on a variable of a built-in datatype using the parentheses syntax always returns a value (or values) of the same datatype!

Put differently, if you imagine a shelf with 5 jars on it. The entire shelf then represents a cell array (by the name of shelf). The expression shelf(3) will then return the third jar of the shelf. On the other hand, the expression shelf{3} returns the content of the third jar!