Question 18 (5 points) You must always include the string.h library if you have any string variables in your program. True False Question 19 (5 points) Which of the following are formatted i/o functions? fgets scanf printf getchar Question 20 (5 points) The term automatic storage duration means The variable has a storage location that exists only as long as its enclosing function exists The variable must be allocated to static (unwritable) memory only The variable never changes value during execution The variable has a permanent storage location Question 21 (5 points) Which of the following is correct about external variables? They have function scope They have automatic storage duration They have file scope They have static duration Question 22 (5 points) The result of the statement a = b++ is: The value of a is the value of b before the increment None of the above The value of b after the increment Either 0 (false) or -1 (true) depending on whether the assignment worked or not Either 0 (false) or 1 (true) depending on whether the assignment worked or not Question 23 (5 points) Which of the following operator symbols have more than one definition, i.e. specify different operations depending on the context of the expression? * +