What is causing "warning: assignment from incompatible pointer type error"?

I'm trying to experiment here with pointer arithmetic, but I get this warning. I am unable to understand where is this going wrong.

The code is written to play with pointer arithmetic since my basics are weak.

    printf("To Check ptrs \t");
    int var[3]={10,20,30};
    int *ptr,i;
    ptr=var;
    for(i=0;i<3;i++)
    {
       printf("Address is %d \t", ptr);
       printf("Value is %d \t", *ptr);
       ptr++;
    }
    ptr=(int*)&var;
    for(i=0;i<3;i++)
    {
       printf("Address is %d \t", &ptr[i]);
       printf("Value is %d \t", ptr[i]);
    }

ptr_arith.c:14:5: warning: assignment from incompatible pointer type [-Wincompatible-pointer-types]
  ptr=&var;
     ^

I got the desired output, though. Also, when I use

ptr=(int*) &var; 

,it doesn't give me any error. So if someone can tell me what's causing it to be "incompatible", I'll be thankful.

It is very simple.

You should arrays decays to pointers in the following way:

int arr[10];

arr is of type int *

&arr[0] - is of type int *

&arr is of type pointer to the array of 10 integers.

In your code you shuld use

ptr = var or ptr = &var[0] as var and &var[0] have the same type as pointer ptr.

&var different type, thus the warning.