PHP does not require (or support) explicit type definition in variable declaration; a variable's type is determined by the context in which that variable is used. That is to say, if you assign a string value to variable $var, $var becomes a string. If you then assign an integer value to $var, it becomes an integer.
An example of PHP's automatic type conversion is the addition operator '+'. If any of the operands is a float, then all operands are evaluated as floats, and the result will be a float. Otherwise, the operands will be interpreted as integers, and the result will also be an integer. Note that this does NOT change the types of the operands themselves; the only change is in how the operands are evaluated.
If the last two examples above seem odd, see String conversion to numbers.
If you would like to test any of the examples in this section, you can use the var_dump() function.
Note: The behaviour of an automatic conversion to array is currently undefined.
Since PHP (for historical reasons) supports indexing into strings via offsets using the same syntax as array indexing, the example above leads to a problem: should $a become an array with its first element being "f", or should "f" become the first character of the string $a?
The current versions of PHP interpret the second assignment as a string offset identification, so $a becomes "f", the result of this automatic conversion however should be considered undefined. PHP 4 introduced the new curly bracket syntax to access characters in string, use this syntax instead of the one presented above:String access by character for more information.
Type casting in PHP works much as it does in C: the name of the desired type is written in parentheses before the variable which is to be cast.
The casts allowed are:
(int), (integer) - cast to integer
(bool), (boolean) - cast to boolean
(float), (double), (real) - cast to float
(string) - cast to string
(array) - cast to array
(object) - cast to object
Note that tabs and spaces are allowed inside the parentheses, so the following are functionally equivalent:
Note: Instead of casting a variable to string, you can also enclose the variable in double quotes.
It may not be obvious exactly what will happen when casting between certain types. For more info, see these sections: