1. Pointers 1 Pointers Pointers  In chapter three we looked at passing parameters to functions using call by value, and using call by reference, using reference variables (&x)  We can also pass parameters using pointer variables to simulate call by reference and to pass dynamic data structures (data structures that grow and shrink during runtime).  Pointer variable declaration and initialization: int y=5; int *yPtr; yPtr = &y; cout << *yPtr; cout << y; *yPtr = 9; cin >> *yPtr  Pointers need to be initialized when they are declared, or in an assignment statement.  A pointer may be initialized to 0, NULL, or an address.  In C++ style, 0 seems to be preferable to NULL.

2. Pointers 2 #include #include using std::cout;using std::endl; int main ( ) { int a = 7, *aPtr = &a; cout << “The address of a is “ << &a << “\nThe value of aPtr is “ << aPtr; cout << “\n\nThe value of a is “ << a << “\nThe value of *aPtr is “ << *aPtr; cout << “\n\nShowing that * and & are inverses of “ << “each other.\n&*aPtr = “ << &*aPtr << “\n*&aPtr = “ << *&aPtr << endl; return 0 }Output: The address of a is 006AFDF4 The value of aPtr is 006AFDF4 The value if a is 7 The value of *aPtr is 7 Showing that * and & are inverses of each other. &*aPtr = 006AFDF4 *&aPtr = 006AFDF4

3. Pointers 3 Passing by value vs. passing by reference using pointers Passing by value vs. passing by reference using pointers //Cube by value #include #include using std::cout; using std::endl; int cubeByValue( int ); int main ( ) { int number = 5; cout << “The original value of number is “ << number; number = cubeByValue( number ); cout << “\nThe new value of number is “ << number << endl; return 0; } int cubeByValue( int n ) { return n * n * n; }

4. Pointers 4 //Cube by reference using a pointer variable #include #include using std::cout; using std::endl; void cubeByReference( int * ); int main ( ) { int number = 5; cout << “The original value of number is “ << number; cubeByReference ( &number ); cout << “\nThe new value of number is “ << number << endl; return 0; } void cubeByReference( int *nPtr ) { *nPtr = *nPtr * *nPtr * *nPtr; }

5. Pointers 5 The relationship between Pointers and Arrays The relationship between Pointers and Arrays int b [ 5 ], *bptr = b;  bptr == &b [ 0 ]  *( bptr + 3 ) == b[ 3 ]  &b[ 3 ] == bptr + 3  *( b + 3 ) == b [ 3 ]  bptr[ 1 ] == b[ 1 ]  An array name is a constant pointer, so b += 3 is invalid.