C++ Pointers and Structs: Code Examples and Explanations

Posted on Mar 28, 2025 in Computers

C++ Pointers and Structs: Code Examples

Pointer Basics

int x;

int y;

int *p = &x;

int *q = &y;

x = 35; y = 46;

p = q;

*p = 78;

cout << x << endl;

cout << y << endl;

int *p;

int *q;

p = new int;

q = p;

*p = 46;

*q = 39;

cout << *p << endl;

int *p;

int *q;

p = new int;

*p = 43;

q = p;

*q = 52;

p = new int;

*p = 78;

q = new int;

*q = *p;

cout << *p << endl;

Pointer Example 1: Storing Variable Addresses

// This program stores the address of a variable in a pointer.

#include <iostream>
using namespace std;

int main()
{
 double x = 22.6;
 double *p;
 double y;
 p = &x;
 y = *p + 20;

 cout << *p << endl;
 cout << y << endl;
 cout << x << endl;

 cin.ignore(100, '\n');
 cin.get();
 return 0;
}

Pointer Example 2: Indirection Operator

// This program demonstrates the use of the indirection operator.

#include <iostream>
using namespace std;

int main()
{
 int x = 25; // int variable
 int *ptr; // Pointer variable, can point to an int

 ptr = &x; // Store the address of x in ptr

 // Use both x and ptr to display the value in x.
 cout << "Here is the value in x, printed twice:\n";
 cout << x << " " << *ptr << endl;

 // Assign 100 to the location pointed to by ptr.
 // This will actually assign 100 to x.
 *ptr = 100;

 // Use both x and ptr to display the value in x.
 cout << "Once again, here is the value in x:\n";
 cout << x << " " << *ptr << endl;
 return 0;
}

Pointer Example 3: Pointing to Different Variables

// This program demonstrates the ability of a pointer to point to different variables.

#include <iostream>
using namespace std;

int main()
{
 int x = 25, y = 50, z = 75; // Three int variables
 int *ptr; // Pointer variable

 // Display the contents of x, y, and z.
 cout << "Here are the values of x, y, and z:\n";
 cout << x << " " << y << " " << z << endl;

 // Use the pointer to manipulate x, y, and z.

 ptr = &x; // Store the address of x in ptr
 *ptr *= 2; // Multiply value in x by 2

 ptr = &y; // Store the address of y in ptr
 *ptr *= 2; // Multiply value in y by 2

 ptr = &z; // Store the address of z in ptr
 *ptr *= 2; // Multiply value in z by 2

 // Display the contents of x, y, and z.
 cout << "Once again, here are the values of x, y, and z:\n";
 cout << x << " " << y << " " << z << endl;
 return 0;
}

Structs

#include <iostream>
using namespace std;

struct rectangleData
{
 double length;
 double width;
};

double rectArea(double x, double y);
double rectperimeter (double, double);

int main()
{
 rectangleData rect1;

 cin >> rect1.length ;
 cin >> rect1.width ;

 cout << "Rectangle area is " << rectArea(rect1.length, rect1.width) << endl;

 cin.ignore(100, '\n');
 cin.get();

 return 0;
}

double rectArea(double x, double y)
{
 return x*y;
}

Struct Example: Time

// structs/time-1.cpp – Shows simple use of a struct. // Fred Swartz – 2003-09-09

#include <iostream>
using namespace std;

// Define a new type
struct Time
{
 int hours;
 int minutes;
 int seconds;
};

// Prototypes
int toSeconds(Time now);

int main()
{
 Time t;
 cout << "Please enter: hours, mins, seconds: ";

 while (cin >> t.hours >> t.minutes >> t.seconds)
 {
 cout << "Total seconds: " << toSeconds(t) << endl;
 }

 cin.ignore(100, '\n');
 cin.get();
 return 0;
}

// Convert Time struct to seconds
int toSeconds(Time now)
{
 return 3600*now.hours + 60*now.minutes + now.seconds;
}

C++ Pointers and Structs: Code Examples and Explanations