Study Notes PHP (3)

1. In php, functions are not case-sensitive, but variables are case-sensitive

2. Functions can define optional parameters, but if there are multiple optional parameters, the default values ​​​​are consecutive from right to left , the middle cannot be skipped; when using this function, the parameters are from left to right

3. Put the frequently used functions in a file, and then import them with required().

4. The method to determine the data type is as follows:

isset(): //Whether the variable has been declared

empty(): //Whether the variable is empty

defined()://whether the constant has been 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 ): // Detect whether the variable is a number or a numeric string

is_bool(): // Detect whether the variable is a Boolean

is_float(): // Detecting whether the variable is a floating point type has the same usage as is_double and is_real()

is_int(): // Detecting whether the variable is an integer is_integer() has the same usage

is_string(): // Check whether the variable is a string

is_object(): // Check whether the variable is an object

is_array(): // Check whether the variable is an array

is_null (): // Check whether the variable is NULL and whether the value is NULL. It is case sensitive

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