Unit 10 Pointers

When a variable is created in C++, a memory address is assigned to the variable. And when we assign a value to the variable, it is stored in this memory address.

To access it, use the & operator, and the result will represent where the variable is stored:

Example

string food = "Pizza";

cout << &food; // Outputs 0x6dfed4

Note: The memory address is in hexadecimal form (0x..). Note that you may not get the same result in your program.

And why is it useful to know the memory address?

References and Pointers (which you will learn about in the next chapter) are important in C++, because they give you the ability to manipulate the data in the computer's memory - which can reduce the code and improve the performance.

These two features are one of the things that make C++ stand out from other programming languages, like Python and Java.

A pointer however, is a variable that stores the memory address as its value.

A pointer variable points to a data type (like int or string) of the same type, and is created with the * operator. The address of the variable you're working with is assigned to the pointer:

Example

string food = "Pizza"; // A food variable of type string

string* ptr = &food; // A pointer variable, with the name ptr, that stores the address of food

// Output the value of food (Pizza)

cout << food << "\n";

// Output the memory address of food (0x6dfed4)

cout << &food << "\n";

// Output the memory address of food with the pointer (0x6dfed4)

cout << ptr << "\n";

Example explained

Create a pointer variable with the name ptr, that points to a string variable, by using the asterisk sign * (string* ptr). Note that the type of the pointer has to match the type of the variable you're working with.

Use the & operator to store the memory address of the variable called food, and assign it to the pointer.

Now, ptr holds the value of food's memory address.

Tip: There are three ways to declare pointer variables, but the first way is preferred:

string* mystring; // Preferred

string *mystring;

string * mystring;

Get Memory Address and Value

In the example from the previous page, we used the pointer variable to get the memory address of a variable (used together with the & reference operator). However, you can also use the pointer to get the value of the variable, by using the * operator (the dereference operator):

Example

string food = "Pizza"; // Variable declaration

string* ptr = &food; // Pointer declaration

// Reference: Output the memory address of food with the pointer (0x6dfed4)

cout << ptr << "\n";

// Dereference: Output the value of food with the pointer (Pizza)

cout << *ptr << "\n";

Note that the * sign can be confusing here, as it does two different things in our code:

When used in declaration (string* ptr), it creates a pointer variable.
When not used in declaration, it act as a dereference operator.

Watch this video

Practical Assignment - 6

Write a program to create a linked list which continuously stores the user input data into dynamic memory as First-In-First-Out (Queue) structure until the user enters '0' as an input. Create two functions, one to take the number of integer type that the user enters and stores it into a new node, and another one to display the data of the linked list. Repeat the program in a Last-In-First-Out (Stack) structure.

You might want to refer to these videos

Page updated

Google Sites

Report abuse