Study notes PHP (3)

: This article mainly introduces the study notes PHP (3). If you are interested in the PHP Tutorial, refer to it. 1. in php, functions are case-insensitive, but variables are case-sensitive.

2. the function can define optional parameters. However, if multiple optional parameters exist, the default values are from right to left coherent and cannot be skipped. when using this function, the parameters are from left to right.

3. put frequently used functions in a file, and then use required () to import them.

4. determine the data type as follows:

Isset (): // whether the variable has been declared

Empty (): // whether the variable is null

Defined (): // whether the constant has defined define ()

Array_key_exists (mixed key, array search): // check whether the given key name or index exists in the array

Is_numeric (mixed var): // check whether the variable is a numeric or numeric string.

Is_bool (): // checks whether the variable is Boolean.

Is_float (): // check whether the variables are float and is_double, is_real ().

Is_int (): // check whether the variable is the same as the integer is_integer ().

Is_string (): // checks whether the variable is a string.

Is_object (): // checks whether the variable is an object.

Is_array (): // checks whether the variable is an array.

Is_null (): // checks whether the variable is NULL or not.

The above introduces the study notes PHP (3), including the content, hope to be helpful to friends interested in PHP tutorials.