POINTER

• Pointer


  A variable that holds the address of another variable

  
• A pointer is declared using the * operator before an identifier
• Pointer can only 'point' to the value with the same data type

  
• Why use pointers


  • If we want to pass a huge struct or array, it's easier to pass a pointer than the whole thing
  • Pointers allow cleaner, more compact code
• Assigning the address of variable to pointer

  1. C++ allows two ways of accessing variables: Name (Identifier) and Address (Pointer)

  2. Symbol & gets the address of the variable that follows it

  3. Addresses can be displayed by the cout statement

  4. Addresses displayed in HEXADECIMAL

  
• Pointer initialization


  • int myvar = 10;

  int * myptr = &myvar;

  int myvar = 10;

  int * myptr;

  myptr = &myvar;
• Pointer Operators


  *: Dereferencing operator - To get the value stored in the memory address

  &: Reference operator / Address-of - Returns the memory address of its operand

  
• Pointer Operators


  • If a number variable is stored in the memory address 0x123, and it contains a value 5. The reference (&) operator gives the value 0x123, while the dereference (*) operator gives the value 5.

  
• Using pointers in C++

  • Define a pointer variable

  2. Assign the address of a variable to a pointer

  3. Access the value at the address available in pointer

  
• Using pointers in C++


  • Example 1:

  int *p, var=101;

  p = &var;

  cout<<*p;

  Output: 101

  
• Using pointers in C++


  • Example 2:

  int firstvalue, secondvalue;

  int * mypointer;

  mypointer = &firstvalue;

  *mypointer = 100;

  mypointer = &secondvalue;

  *mypointer = 200;

  cout << "firstvalue is " << firstvalue << '\n';

  cout << "secondvalue is " << secondvalue << '\n';

  Output: firstvalue is 100, secondvalue is 200
• Using pointers in C++

  • Example 3:

  int *pc, c;

  c = 5;

  cout << "Address of c (&c): " << &c << endl;

  cout << "Value of c (c): " << c << endl << endl;

  pc = &c; // Pointer pc holds the memory address of variable c

  cout << "Address that pointer pc holds (pc): "<< pc << endl;

  cout << "Content of the address pointer pc holds (*pc): " << *pc << endl << endl;

  c = 11; // The content inside memory address &c is changed from 5 to 11.

  cout << "Address pointer pc holds (pc): " << pc << endl;

  cout << "Content of the address pointer pc holds (*pc): " << *pc << endl << endl;

  *pc = 2;

  cout << "Address of c (&c): " << &c << endl;

  cout << "Value of c (c): " << c << endl << endl;

  
• Using pointers in C++


  • Example 4:

  int firstvalue = 5, secondvalue = 15;

  int * p1, * p2;

  p1 = &firstvalue; // p1 = address of firstvalue

  p2 = &secondvalue; // p2 = address of secondvalue

  *p1 = 10; // value pointed to by p1 = 10

  *p2 = *p1; // value pointed to by p2 = value pointed to by p1

  p1 = p2; // p1 = p2 (value of pointer is copied)

  *p1 = 20; // value pointed to by p1 = 20

  cout << "firstvalue is " << firstvalue << '\n';

  cout << "secondvalue is " << secondvalue << '\n';

  
• New Operator


  The "new" operator allocates memory for a variable or any other entity on a heap.
• New Operator


  • int *ptr = NULL; ptr = new int;

  int *p = new int(25);

  float *q = new float(75.25);
• Delete Operator


  The memory allocated dynamically using the new operator has to be freed explicitly by the programmer. For this purpose, we are provided with the "delete" operator.
• Relationship between pointer and array

  Pointers are the variables that hold address. Not only can pointers store address of a single variable, it can also store address of cells of an array.

  
• While assigning the address of array to pointer don't use ampersand sign(&)

  
• Traversing the array using Pointers

  • int *p; int arr[]={1, 2, 3, 4, 5, 6}; p = arr; for(int i=0; i<6;i++){ cout<<*p<<endl; p++;}

  
• Access Array Elements Using Pointer

  • int data[5], *ptr; ptr = data; cout << "Enter elements: "; for(int i = 0; i < 5; ++i) cin >> data[i]; cout << "You entered: "; for(int i = 0; i < 5; ++i) cout << endl << *(ptr + i);

  
• Display address of elements of an array using both array and pointers


  • float arr[5]; float *ptr; cout << "Displaying address using arrays: " << endl; for (int i = 0; i < 5; ++i) { cout << "&arr[" << i << "] = " << &arr[i] << endl; } ptr = arr; // ptr = &arr[0] cout<<"\nDisplaying address using pointers: "<< endl; for (int i = 0; i < 5; ++i) { cout << "ptr + " << i << " = "<< ptr + i << endl; }