Lecture 19

Reading

p.404-414

Pointer

What is pointers?

How to declare pointers?

Example 1: declare pointers 
#include <iostream>
using namespace std;

int main() {
    int *pointer, num = 5 ;
    return 0;
}

Address-of operator

Example 2:Usage of & 
#include <iostream>
using namespace std;

int main() {
    int *pointer, num = 5;
    pointer = &num; // assign the address of num to the pointer
    cout << "The address of num is: "
         << pointer << endl;
    return 0;
}

Output 
The address of num is: 006AFDF0

Dereferencing operator

Example 3: Use dereferencing operator 
#include <iostream>
using namespace std;

int main() {
    int *pointer, num = 5;
    pointer = &num;
    cout << num << endl;
    cout << *pointer << endl;
    return 0;
}

Output 
5
5

More examples

Example 4: What is the output of the following program? 
#include <iostream>
using namespace std;

int main() {
    double *pt, x = 3.15;
    pt = &x;
    cout << x << endl;
    cout << *pt << endl;
    x = 4.2;
    cout << x << endl;
    cout << *pt << endl;
    *pt = 12.59;
    cout << x << endl;
    cout << *pt << endl;
    return 0;
}














Example 5: What is the output of the following program? 
#include <iostream>
using namespace std;

int main() {
    double *pt1, *pt2, x1 = 3.15, x2 = 2.44;
    pt1 = &x1;
    pt2 = &x2;
    cout << x1 << " " << *pt1 << " "
         << x2 << " " << *pt2 << endl;
    pt1 = pt2;
    cout << x1 << " " << *pt1 << " "
         << x2 << " " << *pt2 << endl;
    x2++;
    cout << x1 << " " << *pt1 << " "
         << x2 << " " << *pt2 << endl;  
    pt2 = &x1;
    x1 = 10.7;
    x2 = 2.98;
    cout << x1 << " " << *pt1 << " "
         << x2 << " " << *pt2 << endl; 
    return 0;
}














new operator

Refer to example 6, 7
Example 6: use of new operator 
#include <iostream>
using namespace std;

int main() {
    char *pt;
    pt = new char;
    *pt = 'H';
    cout << *pt << endl;
    return 0;
}

Output 
H








Example 7: What is the output of the following program 
#include <iostream>
using namespace std;

int main() {
    int *p1, *p2;

    p1 = new int;
    *p1 = 42;
    p2 = p1;
    cout << "*p1 == " << *p1 << endl;
    cout << "*p2 == " << *p2 << endl;

    *p2 = 53;
    cout << "*p1 == " << *p1 << endl;
    cout << "*p2 == " << *p2 << endl;

    p1 = new int;
    *p1 = 88;
    cout << "*p1 == " << *p1 << endl;
    cout << "*p2 == " << *p2 << endl;

    return 0;
}