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CAVITE STATE UNIVERSITY
T3 CAMPUS
Department of Information Technology DCIT 25 – Data Structures and Algorithms

Memory allocation before incrementing ptSudentNumber1

What would be the value stored in the pointer variable studentNumber1 if the
studentNumber1 is incremented by 1 using the following statement?
ptStudentNumber1++;

This is tricky because the value of ptStudentNumber1 is 0. If you increment it by
one, the new value is 1. However, memory address 2 is the second half of the memory location
reserved for studentNumber1.This means that ptStudentNumber1 would point to the middle
of the values of studentNumber1, which doesn’t make sense.
That’s not what happens. The computer uses pointer arithmetic. Values are
incremented and decremented in pointer arithmetic using the size of a data type. That is, if the
memory address contains an integer and the memory address is incremented, the computer
adds the size of an integer to the current memory address.

Pointer to Pointers
Imagine having a list of a million students along with their final grades and student
numbers and being asked to sort the list by last name, first name, and student number.
Intuitively, you might think about making two copies of this list, each placed in one of the sort
orders. However, this wastes memory. There is a better approach to sort the list: use pointers
to pointers.
You learned that a pointer is a variable that contains the memory address of another
variable. A pointer to a pointer is also a variable that contains the memory address, except a
pointer to a pointer contains the memory address of another pointer variable.
Let’s begin by declaring four char variables and initializing them with letters of the
alphabet. This is shown in the first statement of the following example. The second statement
declares a pointer called ptInitial and a pointer to a pointer called ptPtInitial. A pointer is
declared using a signal asterisk (*). A pointer is declared using a double asterisk (**).

char initial1 = ‘D’, initial2 = ‘A’, initial3 = ‘C’, initial4 = ‘B’;

char *ptInitial, **ptPtInitial;
ptInitial = &initial1;

ptPtInitial = &ptInitial;

With variables declared, the next two statements assign values to the pointer and to
the pointer to a pointer. In both cases, the ampersand (&) is used as the dereferencing
operator.
The ptInitial pointer variable is assigned the address of variable initial1, which is
memory address 1. The ptPtInitial pointer to a pointer variable is assigned the memory
address of ptInitial. The address of ptInitial is memory address 5.

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