Here are the rules for determine the "truth" of any value not already of the Boolean type −

☛ If the value is a number, it is false if exactly equal to zero and true otherwise.

☛ If the value is a string, it is false if the string is empty (has zero characters) or is the string "0", and is true otherwise.

☛ Values of type NULL are always false.

☛ If the value is an array, it is false if it contains no other values, and it is true otherwise. For an object, containing a value means having a member variable that has been assigned a value.

☛ Valid resources are true (although some functions that return resources when they are successful will return FALSE when unsuccessful).

☛ Don't use double as Booleans.