Practice exercise: Data Typing Functions Categories data: Boolean: this is a logical type. Possible values are true, false. Integer: A data type for integers, or numbers without a decimal point. Floating-point (double, float): A data type for decimal numbers. String: A string is series of characters. Specify by enclosing them in single quotes or double quotes. Testing data types: Test types and validity with the is_* family of functions including: is_null( ), is_int( ), is_string( ), is_double( ), is_bool( ), is_numeric( ), .... 1. Declare variables $nullVar, $intVar, $stringVar, $doubleVar, $boolVar and imply type with assigned values. 2. Use the is_* functions to test the variables from 1. Changing type: Data type may be changed explicity with he function settype( ) with arguments for $variableName and data type. Data types may be 'integer', 'string', 'double', 'bool'. 3. Declare $aVariable, initialized to 1.23, then print its value along with the result from invoking is_double( ). 4. Apply settype( ) to change $aVariable to 'string', 'integer', back to double, and to boolean. After each setting, print its value and the result from invoking the corresponding is_*( ). Type Casting: Changing data type by casting is done by indicating the name of a data type within parentheses in front of a variable name (e.g. (double) $aVar). Casting produces a copy that is converted to the specified type. 5. Declare and intialize $aVar to 4.56. Code a statement to assign $aVar to $temp, then print $temp and the result of is_double($temp). 6. Write additional statements to cast $aVar as a string, an integer, again as a double, and as a boolean, each time assigning the result to $temp. Print $temp and the result of is_double($temp).