how typecasting & dereferencing works here?

#include<stdio.h>
int main(){
    int a, b, c;
    char *p = 0;
    int *q = 0;
    double *r = 0;
    cout<<(int)(p + 1);    // printing 1 char size
    cout<<(int)(q + 1);    // printing 4
    cout<<(int)(r + 1);    // printing 8

    int y = 9;
    int *u = &y;
    cout<<(int)(u+1);       //printing 7208688

   cout<<*(p+1);            //not able to dereferance

   }

How is type-casting working in both the above case?

Why pointers p, q, r are unable to dereference?