Variable Related Functions

Let's look at the functions associated with variables.

Variable Functions	meanings
gettype(variable)	Return data type
settype(variable, Data type to change)	Change data type
intval()	Return data type as integer value
strval()	Return data type as character value
isset()	Determine if variable is declared
unset()	Remove variable
empty()	True if the value of the variable is empty, false otherwise
is_array()	Determine if array
is_double()	Determine if variable type is double
is_bool()	Determine if variable type is boolean
is_integer()	Determine if variable type is integer
is_null()	Determine if variable type is null
is_numeric()	Determine if variable is number
is_object()	Determine if variable type is object

gettype

This function finds what type a variable is.
For example, a string function is a string.
If it is a number, it is a number. And so on. If the number is inside '', do you know that the computer recognizes it as a letter?

<?php
    $var = '3434';
    echo gettype($var).'<br />';
    $var = 3434;
    echo gettype($var).'<br />';
?>

settype

This function changes the type of a variable.
For example, you can change a function of a string to a number and a function of a number to a string.
The example below is a source that replaces the string 98 with a number.

<?php
    $var1 = '98';
    settype($var1, "integer");
    echo gettype($var1);
?>

intval

This function converts a variable value to an integer type.

<?php
    $var1 = 33.232;
    echo intval($var1);
?>

strval

A function that returns a variable as a character value.

<?php
    $var1 = 33;
    $var2 = strval($var1);
    echo gettype($var2);
?>

isset

This function checks whether a variable exists.

<?php
    if(isset($var)){
        echo 'exists variable';
    }else{
        echo 'non-existent variable'';
    }
?>

unset

Function to delete a variable.

<?php
    $var = 'variable';
    if(isset($var)){
        echo 'exists variable';
    }else{
        echo 'non-existent variable';
    }
    echo '<br />';
    echo '<br />';
    unset($var);
    echo 'after using unset <br />';
    echo '<br />';
    echo '<br />';
    if(isset($var)){
        echo 'exists variable';
    }else{
        echo 'non-existent variable';
    }
?>

empty

This function returns true if the value does not exist and false if it exists.

<?php
    $var = ''; // or $var = null; or $var = false

    if(empty($var)){
        echo "empty";
    }else{
        echo "not empty";
    }
?>

is_array

Checks whether a variable type is an array. Returns true if it is an array, false if it is not an array.

<?php
    $arr = array();
    if(is_array($arr)){
        echo "this is array";
    }else{
        echo "not array";
    }
?>

is_double

Returns true if the variable type is double(decimal) and false otherwise.

<?php
    $var = 23234.343;

    if(is_double($var)){
        echo 'Decimal.';
    }else{
        echo "not";
    }

?>

is_bool

Returns true if the variable type is boolean(logical speaker), false otherwise.

<?php
    $var = true;

    if(is_bool($var)){
        echo 'This is a boolean.';
    }
    echo '<br />';
    $var = false;

    if(is_bool($var)){
        echo 'This is a boolean.';
    }
?>

is_integer

Returns true if the variable type is integer(integer) and false otherwise.

<?php
    $var = 1212;
    if(is_integer($var)){
        echo 'integer type.';
    }
?>

is_null

Check if the variable is empty.

<?php
    $var = null;
    if(is_null($var)){
        echo 'The variable has no value.';
    }
 ?>

is_numeric

Check if the variable is empty.

<?php
    $var = 2323.34;
    if(is_numeric($var)){
        echo 'The value of the variable is a number.';
    }
?>

is_object

Check if the variable is empty.

<?php
    class Hello
    {
        public function helloOutput(){
            echo 'hello world';
        }
    }

    $hello = new Hello;

    if(is_object($hello)){
        echo 'This is an object.';
    }else{
        echo 'Not an object';
    }
?>

is_string

Determine if a variable is a string

<?php
    $var = 'I am a string';

    if(is_string($var)){
        echo 'This is a string.';
    }else{
        echo 'Not a string';
    }
?>

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