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Pointer arithmetic in C

In the C programming language, a pointer is an address which stores a numeric value. Hence, a developer can perform several arithmetic operations on the same just as one does on other numerical values. In the concept of arithmetic pointers, four operators can be used such as ++, --, +, and -.

The compiler will allow the user to perform arithmetic operations on pointers which are stored as an alias to a numerical value. Conducting operators using the operators and pointer variables is referred to as an arithmetic pointer.

Since pointers store the address of other variables, they are termed as address data types. These addresses are the memory locations that will be assigned to specific variables, and it never stores any value.

As mentioned, there are few operations allowed within an arithmetic pointer, and these operations differ from those generally used in mathematics.

1. Increment of a pointer: it is a condition that comes under addition. Every time a pointer is incremented, it increments by the number equal to the size of the data type present.

E.g.:

If an integer pointer that stores address 1000 is incremented, then it will increment by 2(size of an int), and the new address will point to 1002. While if a float type pointer is incremented, then it will increment by 4(size of a float), and the new address will be 1004.

#include <stdio.h>
const int MAX = 3;
int main () 
{
int  var[] = {10, 100, 200};
int  i, *ptr;


/* let us have array address in pointer */
ptr = var;


for ( i = 0; i < MAX; i++) 
{
printf("Address of var[%d] = %x\n", i, ptr );
printf("Value of var[%d] = %d\n", i, *ptr );


/* move to the next location */
ptr++;
}


return 0;
}

Output:

Address of var[0] = 9f8312cc
Value of var[0] = 10
Address of var[1] = 9f8312d0
Value of var[1] = 100
Address of var[2] = 9f8312d4
Value of var[2] = 200

2. Decrement of a pointer: It is a condition that also comes under subtraction. When a pointer is decremented, it decrements by the number equal to the size of the data type for which it is a pointer.

E.g.:

If an integer pointer that stores address 1000 is decremented, then it will decrement by 2(size of an int), and the new address will point to 998. While if a float type pointer is decremented, then it will decrement by 4(size of a float),And the new address will be 996.

Address of var[0] = 9f8312cc
Value of var[0] = 10
Address of var[1] = 9f8312d0
Value of var[1] = 100
Address of var[2] = 9f8312d4
Value of var[2] = 200


2.	Decrement of a pointer: It is a condition that also comes under subtraction. When a pointer is decremented, it decrements by the number equal to the size of the data type for which it is a pointer.
E.g.:
If an integer pointer that stores address 1000 is decremented, then it will decrement by 2(size of an int), and the new address will point to 998. While if a float type pointer is decremented, then it will decrement by 4(size of a float),And the new address will be 996.
#include <stdio.h>
const int MAX = 3;
int main () 
{


int  var[] = {10, 100, 200};
int  i, *ptr;


/* let us have array address in pointer */
ptr = &var[MAX-1];


for ( i = MAX; i > 0; i--) 
{


printf("Address of var[%d] = %x\n", i-1, ptr );
printf("Value of var[%d] = %d\n", i-1, *ptr );


/* move to the previous location */
ptr--;
}


return 0;
}

Output:

Address of var[2] = 9f3bb4a4
Value of var[2] = 200
Address of var[1] = 9f3bb4a0
Value of var[1] = 100
Address of var[0] = 9f3bb49c
Value of var[0] = 10

3. Addition of an integer to a pointer: when the pointer is added with a value, this value is then multiplied by the size of the data type and is then added to the pointer.

E.g.:

#include <stdio.h>
int main()
{
	int N = 4;
	int *ptr1, *ptr2;
	ptr1 = &N;
	ptr2 = &N;


	printf("Pointer ptr2 before Addition: ");
	printf("%p \n", ptr2);


	ptr2 = ptr2 + 3;
	printf("Pointer ptr2 after Addition: ");
	printf("%p \n", ptr2);


	return 0;
}

Output:

Pointer ptr2 before Addition: 0x7ffeb89a3bf4 
Pointer ptr2 after Addition: 0x7ffeb89a3c00 

4. Subtraction of integer from a pointer: when the pointer is subtracted with a value, this value is then multiplied by the size of the data type and is then subtracted to the pointer.

E.g.:

#include <stdio.h>
int main()
{
int N = 4;
int *ptr1, *ptr2;
ptr1 = &N;
ptr2 = &N;


printf("Pointer ptr2 before Subtraction: ");
printf("%p \n", ptr2);


ptr2 = ptr2 - 3;
printf("Pointer ptr2 after Subtraction: ");
printf("%p \n", ptr2);


return 0;
}

Output:

Pointer ptr2 before Subtraction: 0x7fffb534a334 
Pointer ptr2 after Subtraction: 0x7fffb534a328 

5. Comparisons of pointers: pointers and other pointers can be compared using some operators known as relational operators such as ==, <, and >.

E.g.:

#include <stdio.h>
const int MAX = 3;
int main () 
{
int  var[] = {10, 100, 200};
int  i, *ptr;
ptr = var;
i = 0;


while ( ptr <= &var[MAX - 1] ) 
{
printf("Address of var[%d] = %x\n", i, ptr );
printf("Value of var[%d] = %d\n", i, *ptr );
ptr++;
i++;
}


return 0;
}

Output:

Address of var[0] = e7e7612c
Value of var[0] = 10
Address of var[1] = e7e76130
Value of var[1] = 100
Address of var[2] = e7e76134
Value of var[2] = 200



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