如何在 PHP 中将字符串转换为数字

### Answer: Use Type Casting
As we know PHP does not require or support explicit type definition in variable declaration. However, you can force a variable to be evaluated as a certain type using type casting.

Let's try out the following example to understand how this works:

```php
<?php
$num = "2.75";
 
// Cast to integer
$int = (int)$num;
echo gettype($int); // Outputs: integer
echo $int; // Outputs: 2
 
// Cast to float
$float = (float)$num;
echo gettype($float); // Outputs: double
echo $float; // Outputs: 2.75
?>
```

You can use (`int`) or (`integer`) to cast a variable to integer, use (`float`), (`double`) or (`real`) to cast a variable to float. Similarly, you can use the (`string`) to cast a variable to string, and so on.

The PHP `gettype()` function returns "double" in case of a float for historical reasons.

Alternatively, you can also use the `intval()` function to get the integer value of a variable.

```php
<?php
echo intval(2);       // Outputs: 2
echo intval(2.75);    // Outputs: 2
echo intval('34');    // Outputs: 34
echo intval('+34');   // Outputs: 34
echo intval('-34');   // Outputs: -34
echo intval(034);     // Outputs: 28
echo intval('034');   // Outputs: 34
echo intval(1e10);    // Outputs: 10000000000
echo intval('1e10');  // Outputs: 10000000000
echo intval(0xff);    // Outputs: 255
echo intval('0xff');  // Outputs: 0
?>
```