php boolean type judgment

 

　　String is true as long as it is not empty and not 0

　　The execution result is

       The execution result is false

       Because === compares not only values, but also types, the output is false. If you use the === sign to compare, it is best to cast the variable to bool type first, otherwise you may not get the desired result

    The number 0 is false

　　empty array is false

　　null is false

　　A variable with a negative value is false