/* Data types convert to each other
* 1 The type is cast
* setType( variable , type ); //int,integer,float,double And so on.
* This function changes the type of the original variable var_dump(); You can look at variables
*
* Used before assignment ( type ) In the form of , It does not change the type of the original variable
* $a=(int)"123abc";
*
* $ variable =intval( Variables or values );
* $ variable =floatval( Variables or values );
* $ variable =stringval( Variables or values );
*
* Note: integers are occupied in memory 4 bytes 2.147e9
* Float in memory 8 bytes
*
*
* 1 The type is automatic conversion ( The most common way ), Variables are automatically converted with the running environment
* Related to variables and types 1 Some common functions
* isset();// judge 1 Is there a variable , Value if it is null It also means empty.
* empty();// judge 1 Are all variables null or not "",null
* unset();// delete 1 A variable
* setType();// Set up the 1 Types of variables
* getType();// To obtain 1 Types of variables var_dump(); Gets the type and value
*
* Variable types test functions
* is_bool();// Determine whether it is Boolean or not
* is_int() is_integer() is_long()// Determine if it is an integer
* is_float(), is_double() is_real()//...
* is_array()
* is_object()
* is_resource()
* is_null()
* is_scalar()// Whether it's a scalar or not
* is_numberic()// To determine whether or not 1 A string of Numbers, or Numbers
* is_callable()// Determines if the function name is valid
* Declaration and use of constants
* 1. Constant is 1 An identifier for a simple value
* 2. A constant cannot be changed or used after it is defined unset() Or some other function cancels
* 3. Constants can be defined and accessed anywhere, regardless of the rules of the variable scope
* 4. Constant use define(" Constant names ", value );
* 5. Constant names are not used when declared or used "$"
* 6. Constant names are always capitalized
* 7. The value of a constant can only be of a scalar type (int,float,bool,string)
* 8. constant 1 You have to give the value when you declare it
* 9.defined(" constant ");// Determine whether constants exist
*
* Predefined constants and magic constants
* echo __FILE__;// Output the current file name directory _ Magic constant
* echo CASE_LOWER;// Output a fixed value _ Predefined constant
*
*/
// This function changes the type of the original variable var_dump(); You can look at variables
$str="100.12345abc";
setType($str,int);
var_dump($str);
// Used before assignment ( type ) In the form of
$str="100.12345abc";
$a=(int)$str;
var_dump($a);// The output int(100)
var_dump($str);// Output value is constant ,"100.12345abc"
// If the string does not start with a number, convert to 0
// Different types of operations
$a=10;
$b="100abc";
$c=true;
$d=12.34;
$sum=$a+$c;// Boolean automatically converts to 1 , the results for 11
$sum=$a+$b;// The results for 110
$sum=$a+$b+$c;// The results for 111
$sum=$a+$b+$c+$d;// The results for 123.34 , because floating point memory space, small memory to large memory.
// Whether it's an array or not
$a=array("one","two",1,3,6,8);
if(is_array($a)){
print_r($a);// Print the array
}else{
echo $a;
}
// Define constants , Use a constant
define("home","this is a home");
$a=100;
function demo()
{
global $a;// because $a It's a global variable so it's called with a global flag
echo $a;
echo home;// Constants can be accessed or defined without regard to scope
}
demo();
// Determine whether constants exist
if(defined("home")
{
echo home;
}
else
{
define("home","this is a home");
}