2.2: How to use a pointer

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How to use a pointer?

Define a pointer variable – you must use an asterisk (*) when defining a pointer variable. All three of the following are valid – they are the same:

- int *ptr;
- int * ptr;
- int* ptr;

Assigning the address of a variable to a pointer using unary operator (&) which returns the address of that variable.
Accessing the value stored in the address using unary operator (*) which returns the value of the variable located at the address specified by its operand.

The reason we associate data type to a pointer is that it knows how many bytes the data is stored in. When we increment a pointer, we increase the pointer by the size of data type to which it points.

how a pointer contains the address of a variable

// C++ program to illustrate Pointers in C++
#include <iostream>
using namespace std;

int main()
{
    int var = 20; 

    // declare pointer variable    
    int *ptr; // assignment happens at time of definition:
                   // it would be: int *ptr = &var;

    // note that data type of ptr and var must be same
    // also note the absence of the * during this assignment
    ptr = &var;    

  

    // assign the address of a variable to a pointer
    cout << "Value at ptr = " << ptr << endl;
    cout << "Value at var =" << var<< endl;
    cout << "Value at *ptr =" << *ptr<< endl;     
    
    return 0;

}

Output:

Value at ptr = 0x7ffcb9e9ea4c
Value at var = 20
Value at *ptr = 20

Adapted from:

"Pointers in C/C++ with Examples" by Abhirav Kariya, Geeks for Geeks is licensed under CC BY 4.0