Pointers and references

Pointers and references
You are encouraged to solve this task according to the task description, using any language you may know.

In this task, the goal is to desmonstrate common operations on pointers and references.

C++

With pointers:

The following code creates a pointer to an int variable

 int var = 3;
 int* pointer = &var;
 // or alternatively:
 int* pointer2(&var);

Access the integer variable through the pointer:

 int v = *pointer; // sets v to the value of var (i.e. 3)
 *pointer = 42; // sets var to 42

Change the pointer to refer to another object

 int othervar;
 pointer = &othervar;

Change the pointer to not point to any object

 pointer = 0;
 // or alternatively:
 pointer = NULL;

Get a pointer to the first element of an array:

 int array[10];
 pointer = array;
 // or alternatively:
 pointer = &array[0];

Move the pointer to another object in the array

 pointer += 3; // pointer now points to array[3]
 pointer -= 2; // pointer now points to array[1]

Access another object in the same array through the pointer

 v = pointer[3]; // accesses third-next object, i.e. array[4]
 v = pointer[-1]; // accesses previous object, i.e. array[0]
 // or alternatively
 v = *(pointer + 3); // array[4]
 v = *(pointer - 1); // array[0]

With references:

The following code create a reference to an int variable:

 int var = 3;
 int& ref = var;
 // or alternatively:
 int& ref2(var);

Access the integer variable through the reference

 int v = ref; // sets v to the value of var, that is, 3
 ref = 42; // sets var to 42

References cannot be changed to refer to other objects, and cannot (legally) made to refer to no object.

Get a reference to the first element of an array:

 int array[10];
 int& ref3 = array[0];

Changing the reference to refer to another object of the array is not possible.

Accessing another object of the array through the reference:

 v = (&ref)[3]; // read value of array[3]; however doing this is bad style

Tcl

Tcl does not have pointers, however if required a similar level of indirection can be had by storing a variable name in another variable, eg.

 set var 3
 set pointer var; # assign name "var" not value 3
 set pointer;     # returns "var"
 set $pointer;    # returns 3
 set $pointer 42; # variable var now has value 42

In practice it's safer and more convenient to use array keys, eg.

 set arr(var) 3
 set pointer var
 set arr($pointer);    # returns 3
 set arr($pointer) 42; # arr(var) now has value 42