Stupid birds Learn PHP (ii) How to use variables

I. Declaration of variables

1. methods of declaring variables in PHP: $var = 123;

2. PHP is a weakly typed language, and the type of the variable is determined by the stored value

Note: Java is a strongly typed language, declaring a variable must first specify the type

3. Isset () and unset ()

Isset (): Determine whether the value exists; Unset (): Remove the value of the variable

<?php $a = $b = $c = $d = "Hello, world"; unset ($a); if (Isset ($a)) {echo $a;} else{echo "not exists";}? >

Two. Naming of variables

1. be sure to use "$" before the variable, declare and use this symbol.

2. You cannot start with a number.

3. Cannot use the arithmetic symbol in PHP +-*/% &

4. You can use the System keyword as the variable name

5. Only variables and constants in PHP are case-sensitive, others do not differentiate

Two. Variable variable

1. variable names for a variable can be set and used dynamically

<?php$one = "AAA"; $two = "one"; $three = "one"; Echo $$ $three;    The result is aaa?>

2. Variable can be referenced assignment (and a reference in Java)

<?php$one = "AAA"; $two = & $one;   With the "&" symbol added to the variable that will be assigned, $one and $two point to the same address $two = "BBB"; Echo $one;? >

Three. Types of variables

1. As mentioned earlier, PHP is a weakly typed language, and its type is determined by the stored value

2. PHP has 8 types:

2.1) Four kinds of scalars:

Shape: int integer Boolean: bool Boolean float: float double real string: string

2.2) Two types of composite

Array: Array object: Object

2.3) Special types in two

Resource type: Resource NULL type: null

<?php$var=10;var_dump ($var); Int (Ten) $var =34.5;var_dump ($var); Float (34.5) $var = "abc"; Var_dump ($var); String (3) "ABC" $var =true;var_dump ($var); BOOL (true) $var =array, Var_dump ($var); Array (3) {[0]=>int (1) [1]=>int (2) [2]=>int (3)} $var =new mysqli ("localhost", "root", "root", "newcms"); var_ Dump ($var); Object (mysqli) #1 (0) {} $var =fopen ("1.php", "R"), Var_dump ($var); Resource (3) of type (stream) $var =null;var_dump ($var); Null?>

Four. Variable declarations of various types

The maximum value of <?php//integer is 4 bytes, 2 of 32 times, 214483647$int=10;   Decimal statement $int=045;  The expression starting with 0 declares a variable $int=0xff in 8 notation; The representation beginning with 0x or 0X declares a variable 0-9 a-f 0X a-f$int=-5 in 16 notation;   $float =10, $float =-10, $float =3.14e5; $float =3.15e+5; $float =5.14e-2;  E can be uppercase or lowercase//the following is false case $bool=false;   true$bool=0;       Number of $bool=0.000 not 0;   There are not 0 of the number appearing $bool= "";      $bool = "";     $bool =null;    Non-null representative $bool= "0";     Non-null non-0 string $bool=array (); There are members of the array//Expression true: True, not 0 of the number, there are non-0 of the number of occurrences, non-null represents, non-null non-0 string, there are a number of members of the array//string declaration There are several ways//1. Both single and double quotes can declare strings, and the declared string has no length String, you can directly parse the variable, or you can directly use the escape character//3. In a single-quoted string, you cannot parse a variable, or you can use an escape character (you can escape the single quotation mark itself, or you can escape the escape character "\")//4. Double quotes are no longer used in double quotes. Single quotes can no longer be used in single quotes $str= ' aaaaa\ ' aaa '; $str = "aaaa\" AAAA "; $str =<<<one one; $str = ' dir ';? >