Pointer operations

Just like any other data type, we can perform various arithmetic operations on pointers.

All pointers int, float, long, and double are 2 bytes on a 16-bit machine.

When we perform any arithmetic function, such as increment on a pointer, the size of their primitive data type changes.

Remember the following data type storage sizes in a 16 bit machine:

C Data types / storage Size	Range
char / 1	–127 to 127
int / 2	–32,767 to 32,767
float / 4	1E–37 to 1E+37 with six digits of precision
double / 8	1E–37 to 1E+37 with ten digits of precision
long double / 10	1E–37 to 1E+37 with ten digits of precision
long int / 4	–2,147,483,647 to 2,147,483,647
short int / 2	–32,767 to 32,767
unsigned short int / 2	0 to 65,535
signed short int / 2	–32,767 to 32,767
long long int / 8	–(2power(63) –1) to 2(power)63 –1
signed long int / 4	–2,147,483,647 to 2,147,483,647
unsigned long int / 4	0 to 4,294,967,295
unsigned long long int / 8	2(power)64 –1

Pointer Arithmetic Examples:

int* a;
a++;

In the preceding example, the pointer will be two bytes long. When we increment it, it will increase by two bytes because int is also two bytes.

For instance:

#include<stdio.h>
int main()
{

   int  b;
   int  *p;
   int  **ptr;

   b = 10;

   /* take the address of b */
   p = &b;

   /* take the address of p using address of operator & */
   ptr = &p;

   /* take the value using ptr */
   printf("Value of b = %d\n", b );
   printf("Value available at *p = %d\n", *p );
   printf("Value available at **ptr = %d\n", **ptr);
    /* take the address  */
   printf("Value of &b = %u\n", &b );
   printf("Value available at p = %u\n", p );
   printf("Value available at ++p = %u\n", ++p );
    printf("Value available at ptr = %u\n", ptr);
    printf("Value available at ++ptr = %u\n", ++ptr);

   return 0;
}

Output:

/tmp/L66gawGDLh.o
Value of b = 10
Value available at *p = 10
Value available at **ptr = 10
Value of &b = 1618367364
Value available at p = 1618367364
Value available at ++p = 1618367366
Value available at ptr = 1618367368
Value available at ++ptr = 1618367380

Here, we can clearly see that the value of ++p and ++ptr is incremented by 2 bytes. Similarly, the value is increased in proportion to their size.

If we used a four-bit machine, the same output would have been incremented by four bytes for integer data.

Note: also read about the Pointer to Pointer in C

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