U3_4_PointerArithmetic.pdf people will use the above preaentationa dn

UNIT III
Modular programming:
Function prototype
Function definition
Function call
Built-in functions
Recursion:
Recursive functions
Pointers:
Pointer increment
Pointer arithmetic
Parameter passing:
Pass by value
Pass by reference
Pointer and arrays
Dynamic memory allocation with malloc/calloc
Topics to be Covered:
12/13/2023 1
BVL_Computer Centre, Madras Institute of Technology

Address in C
• Whenever a variable is defined in C, then we can access the
memory address of that variable using & symbol.
• For example, if we define a variable named num then if we
use &num, it will give the variable num’s address in memory.
12/13/2023 2
Output:

Pointers in C
• Pointers are variables that store the address of other variables.
• A pointer can be used to store the memory address of other
variables, functions, or even other pointers.
• The use of pointers allows low-level memory access, dynamic
memory allocation, and many other functionality in C.
12/13/2023 BVL_Computer Centre, Madras Institute of Technology 3

Pointer declaration
• Like ordinary variables, pointers also have a data type and
must be declared before they are used to store the address
of any variable.
• Pointers are declared with the help of an asterisk (*)
followed by the pointer's name.
• Syntax:
datatype *pointer_variable_name;
• In the above syntax, type refers to what data
type of the variable the pointer will point
to.
• All the pointers, whether integer, float, character, etc., are
of the same data type, a long hexadecimal number
representing the memory address.

Pointer declaration – Cont’d
• Pointers can be declared in two ways:
• One way is to attach the asterisk with the name of the pointer
variable during the declaration
• i.e. datatype *pointerVariable
• Example: int *ptr;
• Another way is to attach the asterisk at the end of the data
type of which the pointer variable is to be created
• i.e. datatype* pointerVariable
• Example: int* ptr;

• In the previous example, ptr is a pointer, and its type
will be specifically be referred to as "pointer to int",
because it stores the address of an integer variable.
• The type is important.
• While pointers are all the same size, as they just store
a memory address, we have to know what kind of
thing they are pointing to.
• double * dptr; // a pointer to a double
• char * cptr; // a pointer to a character
• float * fptr; // a pointer to a float

• Recall that we can declare multiple variables on one line
under the same type, like this:
int x, y, z; // three variables of type int
• Since the type of a "pointer-to-int" is (int *), we might ask,
does this create three pointers?
int* a, b, c;
• This is not three pointers. Instead, this is one pointer and
two integers.
• If we want to create multiple pointers on one declaration,
we must repeat the * operator each time:
int * a, * b, * c; // three pointers-to-int
• int * a, b, c; // a is a pointer, b and c are integers.

Initialize a pointer
• After declaring a pointer, we should initialize it like
standard variables with a variable address.
• In C programming, If pointers are uninitialized and used in
the program, then the results are unpredictable and
potentially disastrous.
• Syntax:
pointer = &variable;
• Example: ptr=&num;
• Note:
• Pointer values and integer values are entirely different
• We cannot store any address in integer variable.
• To store address of any variable we have to declare one variable
as pointer.

Output:
Note: In our program pointer variable ptr
contains the address of integer variable num.
To store address of float, char or any other type
variable, we have to declare a pointer of that
type.

Accessing address of register variable
• In the above program, the code tries to get the address of variable
i into the pointer variable p but as i is declared as a register
variable, the code won’t compile and will display the error ” Error:
address of register variable requested”.
• Only certain types of variables are placed into registers.
• Register variables are not given an initial value by the compiler.

* value at address Operator
(dereference operator)
• This is the second operator used for pointers.
• It is used to access the value present at some address.

Output:

UNIT III
Modular programming:
 Function prototype
 Function definition
 Function call
Built-in functions
Recursion:
 Recursive functions
Pointers:
Pointer increment
Pointer arithmetic
Parameter passing:
 Pass by value
 Pass by reference
Pointer and arrays
Dynamic memory allocation with malloc/calloc
Topics to be Covered:
12/13/2023 13

Pointer Arithmetic
• We can perform arithmetic operations on the pointers
like addition, subtraction, etc.
• The C language allows following operations to be
performed on pointers.
• Increment/Decrement of a Pointer.
• Addition/Subtraction of Integer to a Pointer.
• Differencing (Subtraction of two Pointer of similar type)
• Comparison of two Pointer of similar type.
12/13/2023 14

Pointer Increment
• If we increment a pointer by 1, the pointer will start pointing
to the immediate next location.
• This is somewhat different from the general arithmetic since
the value of the pointer will get increased by the size of the
data type to which the pointer is pointing.
• The Rule to increment the pointer is given below:
Next_address= current_address + size_of(data type)
• In 32-bit Machine:
• int variable, it will be incremented by 2 bytes.
• int variable, it will be incremented by 4 bytes.
• Similarly, a pointer to a float will be incremented by
sizeof(float) and pointer to char will be incremented by
sizeof(char) .
12/13/2023 15

Pointer Increment
Output:

Pointer decrement
• Decrementing a pointer in C simply means to decrease the
pointer value step by step to point to the previous location.
Previous Address = Current Address – size_of(data type)
• Decrementing a pointer to an int will cause its value to be
decremented by sizeof(int).
• int variable, it will be decremented by 2 bytes.
• int variable, it will be decremented by 4 bytes.
• Similarly, a pointer to a float will be decremented by
sizeof(float) and pointer to char will be decremented by
sizeof(char) .
12/13/2023 17

Pointer decrement
Output:

Addition/Subtraction of Integer to a Pointer
• C allows integers to be added to or subtracted from pointers.
• When an integer i is added to the pointer, then the new value will
be,
(current address in pointer) + i * sizeof(data_type)
• Example:
• int *ptr, n=20; ptr=&n; ptr=ptr+3
• This code will increment the address in ptr by 3*sizeof(int).
• If the sizeof(int) is 4, then the pointer will increment by 12.
• n=20 and ptr=1000 after ptr=ptr+3 value of ptr becomes 1012.
• Likewise when an integer i is subtracted from a pointer, the the
new value will be,
(current address in pointer) – i * sizeof(data_type)
• Example:
• int *ptr, n=20; ptr=&n; ptr=ptr-3
• This code will decrement the address in ptr by 3*sizeof(int).
• If the sizeof(int) is 4, then the pointer will decrement by 12.

Addition/Subtraction of Integer to a Pointer
Output:

Subtracting of two pointers of similar type
(Differencing)
• Differencing is the subtraction of two pointers.
• Subtraction of two pointers is only possible, if they have
same data type.
• When two pointers of same data type is subtracted , their
value is subtracted then result will be divided by the size of
data type.
(address in pointer1 - address in pointer2) / sizeof(data_type)
• If 2 pointers points to 2 different array index of same array
then the subtraction of two pointers gives the number of
elements between the two pointers.
• Example:
int a[5] = {10,20,30,40,50};
int *p, *q;
p=&a[0]; q=&a[3];
printf(“%d”, q-p);
The output of q-p will be (1012-1000)/sizeof(int) i.e 12/4=3.

Differencing
Output:

Comparison of two pointers of similar
type
• Comparison of two pointers is only possible, if they have
same data type.
• Two pointers can be compared by the operators >, ==,
<= , >=.
• It returns TRUE if condition valid, otherwise return
FALSE.

Comparison of two pointers of similar type
Output:

U3_4_PointerArithmetic.pdf people will use the above preaentationa dn

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