Introduction to conversion between data types in PHP learning

Copy CodeThe code is as follows:
/* data types are converted to each other
* One is a cast
* SETTYPE (variable, type); Int,integer,float,double and so on.
* This function changes the type of the original variable, with Var_dump (), you can view the variable
*
* Use the form of (type) before assigning, without changing the type of the original variable
* $a = (int) "123ABC";
*
* $ variable =intval (variable or value);
* $ variable =floatval (variable or value);
* $ variable =stringval (variable or value);
*
* Note: The integral type occupies 4 bytes in memory 2.147e9
* Floating-point type occupies 8 bytes in memory
*
*
* One is automatic conversion (the most common way), the variable will be more operational environment automatic conversion

* Some common functions related to variables and types
* Isset ()//To determine whether a variable exists, the value if NULL also indicates null.
* EMPTY ()//To determine whether a variable is empty "", null
* unset ()//Delete a variable
* SetType ()//Set a variable type
* GetType ()//Get a variable type var_dump (); Get type and value
*
* Variable type test function
* Is_bool ()//To determine whether the Boolean type
* Is_int () Is_integer () Is_long ()//To determine whether it is an integral type
* Is_float (), is_double () is_real ()//...
* Is_array ()
* Is_object ()
* Is_resource ()
* Is_null ()
* Is_scalar ()//To determine whether the scalar
* Is_numberic ()//judge whether it is any kind of number, or numeric string
* Is_callable ()//To determine whether a valid function name

* Declaration and use of constants
* 1. A constant is an identifier for a simple value
* 2. The constant definition can no longer change its value, nor can it use unset () or other functions to cancel
* 3. Constants can be defined and accessed anywhere by ignoring the rules of variable scope
* 4. Constants using define ("Constant name", value);
* 5. The constant name does not use "$" when declared and used
* 6. Constant name habits all use uppercase
* 7. The value of a constant can only be scalar type (int,float,bool,string)
* 8. Constants must be given the value at the time of declaration
* 9.defined ("constant");//To determine whether a constant exists
*
* Predefined Constants and Magic constants
* Echo __file__;//output Current file name Directory _ Magic constant
* echo case_lower;//Output Fixed value _ predefined constants
*

*/
This function changes the type of the original variable, using Var_dump (), and can view the variable
$str = "100.12345ABC";
SetType ($str, int);
Var_dump ($STR);

Use the form of (type) before assigning a value
$str = "100.12345ABC";
$a = (int) $str;
Var_dump ($a);//output int (100)
Var_dump ($STR);//output value unchanged, "100.12345ABC"
If the string does not begin with a number, it is converted to 0

Different types of operations
$a = 10;
$b = "100ABC";
$c =true;
$d = 12.34;
$sum = $a + $c;//Boolean automatically converted to 1, the result is 11
$sum = $a + $b;//The result is 110
$sum = $a + $b + $c;//The result is 111
$sum = $a + $b + $c + $d;//The result is 123.34, because of the large floating-point memory space, small memory to large memory.

To determine whether it is an array
$a =array ("One", "two", 1,3,6,8);
if (Is_array ($a)) {
Print_r ($a);//print array
}else{
echo $a;
}

Defining constants, using constants
Define ("Home", "This is a Home");
$a = 100;
Function Demo ()
{
Global $a;//Because $a is a global variable, call
echo $a;
The Echo home;//constant can be accessed or defined directly, regardless of the scope
}
Demo ();

To determine whether a constant exists
if (Defined ("Home")
{
Echo home;
}
Else
{
Define ("Home", "This is a Home");
}