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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 double, then all operands are evaluated as doubles, and the result will be a double. 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.
$foo = "0";                                    // $foo is string (ASCII 48)
$foo++;                                        // $foo is the string "1" (ASCII 49)
$foo += 1;                                    // $foo is now an integer (2)

$foo = $foo + 1.3;                        // $foo is now a double (3.3)
$foo = 5 + "10 Little Piggies";      // $foo is integer (15)
$foo = 5 + "10 Small Pigs";         // $foo is integer (15)
If the last two examples above seem odd, see String conversion.
If you wish to force a variable to be evaluated as a certain type, see the section on Type casting. If you wish to change the type of a variable, see settype.