A definitive guide to PHP development

Declaration and naming of 3.2.1 variables

1<?PHP2     $title= "Hello";//correct3     $title 123= "Hello";//correct4$123title= "Hello";//Error5     $_title= "Hello";//correct6[Email protected]#title= "Hello"; Error7     $url= "Hello";//we get a variable URL8     Echo $url;//Result: Hello9     unset($url);//delete a variable URLTen     Echo $url;//result is empty One?>

3.2.2 variable variable and reference assignment

1 <? PHP 2     $var= "php"; 3     $php= "Hello"; 4     Echo $var;   // Output result php 5     Echo $$var;   // Output Result Hello 6 ?>

3.3.1 String

1<?PHP2     $title= "Hello"; 3     Echo' $title, World ';//results: $title, World4     Echo"$title, World ";//results: Hello,world5     Echo"${title},world";//results: Hello,world6     Echo"{$title},world ";//results: Hello,world7     Echo"\ $title, World";//results: $title, World8?>

Casting and application of 3.3.8 type

//convert other types to integral type<?PHP$php=100.10; Echo(int)$php;//Output Result:    $php=true; Echo(int)$php；//output results: 1    $php= "123php"; Echo(int)$php;//output Result: 123    $php= "Php123"; Echo(int)$php;//output results: 0?>//other types are converted to String type<?PHP$php=100.1; Var_dump((string)$php);//Output: String (4) "100.1"    $php=true; Echo(string)$php;//output results: 1?>//other types are converted to floating-point type<?PHP$php= "123.2php"; Var_dump((float)$php);//output Result: float (123.2)    $php= "php123.2"; Var_dump((float)$php);//output results: (0)?>//Other types convert to Boolean<?PHP$php= "PHP"; Var_dump((BOOL)$php);//Output Result: bool (TRUE)    $php=0; Var_dump((BOOL)$php);//Output Result: bool (false)?>

A definitive guide to PHP development