pointer: a value that refers to another object
    non-null-pointer:  a pointer whose value is not zero
    string:  a sequence of characters in format F
    sp:  a pointer to a string
    nnsp:  a non-null-pointer to a string
    boolean:  TRUE | FALSE

    boolean strcmp (nnsp a, nnsp b):  takes two non-null 
        string pointers and returns TRUE if the strings are equal