Solution to Homework #1

1.1 Name and illustrate 5 operations that can be applied to pointers.
    +,-,*,/ : arithmatic         : p + q
    *  : dereferencing operator  : *ptr  
    ++ : increment or decrement  : ++p
    == : equality                : p == q
    =  : assignment              : p = &a

1.2 Consider

int A, B; 
int *Ptr;
int **PtrPtr;

Ptr = &A;
PtrPtr = &Ptr;

a. Is this legal?
   :YES
b. What are the values of *Ptr and **PtrPtr?
   :Both have the value of A.
c. Using no other objects besides those declared above, how can we alter
   PtrPtr so that it points at a pointer to B without directly touching Ptr?
   : *PtrPtr = &B
d. Is the following legal? PtrPtr = Ptr
   : NO, it is the type-mismatch.

1.3. Answer the following:
a. Is *&X always equal to X? If not, give an example.
   :YES

Explanation: because *&X gives the value of X not matter what type X is 
declared to be, and the address of X is always defined, so &X can 
have the derefence operator * applied.

b. Is &*X always equal to X? If not, given an example.
   :NO, if X is defined as INT, then *X is not defined. 


1.4 For the declarations

int A = 5;
int *Ptr = &A;

What are the values of the following?

a. Ptr
   :  &A
b. *Ptr
   :  5
c. Ptr == A
   :  Illegal, type-mismatch.
d. Ptr == &A
   :  TRUE
e. &Ptr
   :  address of Ptr
f. *A
   :  error
g. *&A
   : 5
h. **&Ptr
   : 5

1.5 Give the types of all the identifiers declared here and the types of the
expressions. Is any expression illegal?

a. struct S {
        int A;
        S *B;
   };
   : S is a struct type consisting of two member; A of type integer, and
     B of type pointer to struct S.
b. S Z;
   : Z is declared as a struct of type struct S.
c. S *X;
   : X is declared as a pointer to struct S.
d. S Y[10];
   : Y is an array of size 10 of struct S.
e. S *U[10]
   : U is an array of size 10 of pointer to type struct S.
f. X->A
   : value of int member of struct X. A is integer
g. X->B
   : member B of struct X, and B is a pointer to type struct S
h. Z.B
   : member B of Z of type struct S. B is a pointer to struct S.
i. Z.A
   : value of member A of Z of type struct S. A is integer
j. *Z.A
   : Illegal expression. Z.A is not a pointer
k. (*Z).A
   : Illegal expression. Z is not a pointer.
l. X->B-Z.B
   : pointer arithmatic
m. Y->A
   : integer member of first struct in array Y.
n. Y[1]
   : the second element of array Y.
o. Y[1].A
   : integer member of the second element of array Y.
p. Y[1].B
   : pointer member of the second element of array Y.
q. U[2]
   : pointer to struct S
r. *U[2]
   : dereferencing a pointer to struct S
s. U[2]->A
   : integer member of a struct of type struct S which is pointed to
     by U[2]
t. U[2]->B
   : pointer member of a struct of type struct S which is pointed to 
     by U[2]
u. U[10]
   : pointer to a struct of type struct S. The compiler will compile 
     this even though it is out of range.
v. &Z
   : address of Z.
w. &X
   : address of X.  
x. U
   : pointer to the first element of array U.
y. Y
   : pointer to the first element of array Y.

1.6 Draw a picture that illustrates the results after each of the following
statements, which are executed sequentially.
  int A = 3;      (1)
  int& B = A;     (2)
  int& C = B;     (3)
  B = 5;          (4)
  C = 2;          (5)

    : After (1), A = 3
      After (2), B = A = 3
      After (3), C = B = A = 3
      After (4), C = B = A = 5
      After (5), C = B = A = 2

1.7 Do you think the following is legal? Why or why not?

int A = 3;
const int& B = A;
: It is legal, however, it is considered a bad programming because
  B is declared constant but if the value of A is changed, B's value
  is also changed.


1.8 What is wrong with omitting spacing in the following

*X/*Y

: If there is no space between / and *, then Y will be ignored because
  compiler consider /* as the start of the comment.