PHP Syntax Basics

PHP Data type (it is a weakly typed language)

Integer, floating-point, Boolean, String, array, object, NULL type, resource-type

Scalar type: integer, Float, Boolean, and String type! The so-called scalar types, in essence, can only store the type of individual information.

Compound: Array, object. The essence of composite types is that you can store multiple information!

Special type: null type and resource type

All types are stored in binary form in the computer!

Binary conversions:

Decimal conversion to binary: Multiply by 2 rounding method

Ten ext. Eight: Integer part in addition to eight remainder, fractional division by eight rounding

Octal is converted to binary and can be split three:

Binary conversion to octal can be three and one:

16 binary conversion to binary, you can split four:

Binary conversion to 16 binary can be four and one:

Eight ext. 16: First split three conversions to two, then four and one converted to 16:

16 ext. Eight: First split four converted to two, and then repeatedly and one converted to eight

Exponential form:

A few things to note:

1, E is case insensitive

2, there must be numbers before and after E.

E must be followed by an integral type

Integer data is stored in memory in the form of a second-order complement!

Positive number (symbol 0) of the original code, anti-code, the same complement

The inverse of a negative number (symbol 1) is on the basis of its original code, in addition to the symbol bit unchanged, the rest of the bitwise negation,

Complement of negative number = Its anti-code +1

Convert to Boolean, and a few will be converted to false:

Integral type 0:0

Floating point 0:0.0

String 0: ' 0 '

Empty string: ' "

NULL type: null

Empty array: Array ()

Resource type and object type are always true!

The difference between single and double quotes in PHP:

Single quote: Cannot recognize variable, escape character

Double quotes: Ability to recognize variables, escape characters

Delimiter:

Syntax:<<< start tag

Content

end tag;

The start tag and the end tag need to be consistent, and the tag is defined by itself. The end tag of the delimiter must be shelf written!

Type-dependent functions:

GetType () Gets the data item type

Settype () Sets the type of the variable

Isset () Determine if a variable exists

Empty () to determine if the variable is null

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