Question

#include<stdio.h>
#include<stdlib.h>

int main ()
{
   int a[]={0,1,2,3,4};
   int *p[]={a,a+1,a+2,a+3,a+4};
   int **ptr=p;

   ptr++;
   printf("%d %d %d\n",ptr-p,*ptr-a,**ptr);

   *ptr++;
   printf("%d %d %d\n",ptr-p,*ptr-a,**ptr);

   *++ptr;
   printf("%d %d %d\n",ptr-p,*ptr-a,**ptr);

   ++*ptr;
   printf("%d %d %d\n",ptr-p,*ptr-a,**ptr);
return 0;
}

The answer for this program is
1 1 1

2 2 2

3 3 3

3 4 4

with gcc.But why is the output for the first printf giving 1 1 1 shouldn’t it be 4 4 1?
lets say if p=6004 and and ptr would be 6004 and ptr++ would be 6008.then ptr-p should give 4.pls correct me.thanks..

Answer 1

The result of pointer arithmetic is not exactly the result of their address arithmetic. The output should be ((address of ptr) - (address of p)) / (sizeof(pointed_type))
For example:

int a[] = {0,1,2,3,4};
int *p=a;
int *p2 = p+1;
printf("%d",p2-p)     // will print 1