Oracle Database Tips by Donald Burleson

Data types

PHP is weakly typed language and variables can be of any type.  The first item that deserves mention is the string NULL in the example above. Variable NULL literally means, "the absence of value".  Saying that the variable has the NULL value is the same as saying that the variable has no value.

Variables that do have values usually represent numbers, strings or resources. Variables that represent numbers are represented by strings of digits, with or without the decimal point. Numbers can also be written using an engineering notation in which the number 13500 would be written as 1.35e4, octal or hexadecimal notation. 

The leading zero means the number is written using octal notation, while prefix "0x" is used for hexadecimal notation. For example, the expression $a=0100; would set the variable $a to decimal value of 64 (octal notation), while the expression $a=0x100; would set the variable $a to the decimal value of 256 (hexadecimal notation).

Boolean Values

In addition to numbers, most programming languages recognize Boolean values and distinguish between TRUE and FALSE statements. Conventions in PHP are very similar to those in Perl or C.  The following list shows FALSE values:

§         0
§         "0"
§         0.0
§         NULL
§         array()
§         "" (empty string)
§         The keyword "FALSE"

Any value that is not FALSE is TRUE. The usual logical operators apply and have the usual precedence identical to the definitions in other languages. It is worth noting that in contrast to SQL which adopted the ternary logic in which the NULL value is neither TRUE nor FALSE, PHP remained TRUE to the classic binary logic.

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