Why is there no 5 in the php array subscript?

In PHP, an array is an ordered data collection, consisting of one or more key-value pairs, and the subscript of the key-value pair is used as the index of the array. In an array, each element has a unique index, and the unique index can be a numeric value, a string, or other types.

However, we often encounter such a problem: Why does the PHP array not have the subscript 5?

Actually, there can be a subscript of 5 in the PHP array, but in some cases it may be ignored or overwritten by other subscripts.

The reasons are as follows:

1. The starting subscript starts from 0

In PHP, the starting subscript of the array starts from 0, not from 1 start. Therefore, when we declare an array, the index of the first element of the array is 0, not 1. This is why we often see PHP programmers use $my_array[0] to represent the first element of the array.

2. Automatic type conversion

PHP is a dynamically typed language, which will automatically convert the type of variables. This means that when we use a non-numeric string subscript as an array index, PHP will automatically convert it to an integer type. For example, the following code:

$my_array["hello"] = "world";

echo $my_array["hello"]; //Output "world"

echo $my_array[0]; //Output "world"

Here, we use the string "hello" as the subscript of the array, but this string does not have a value, so PHP converts it to 0 , so $my_array[0] will output "world".

3. Other subscripts may cover 5

Another reason is that in some cases, other subscripts of the array may cover the 5 subscript. For example, in the following code:

$my_array = array(0, 1, 2, 3, 4, "five" => 5, 6);

echo $my_array[ 5]; //Output ""

Here, we set the value of the element with the subscript "five" to 5. Since "five" is not a numeric subscript, its index in the array is associative, not numeric. Therefore, in this array, the index 5 is already occupied by the associated index "five", so $my_array[5] will output an empty string.

Summary:

In PHP, arrays can have any index, including numeric, string, associative and other types. Array subscripts start counting from 0, and PHP will automatically perform type conversion, so we can use strings, floating point numbers and other types as array indexes. At the same time, in an array, multiple elements can share the same subscript, such as an associative array. Therefore, even if there is no element with array index 5, we can access the element at this position through other methods.

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