c - Storing Pointers difference in integers? -

this code:

#include<stdio.h> #include<conio.h>  int main() {     int *p1,*p2;     int m=2,n=3;     m=p2-p1;     printf("\np2=%u",p2);     printf("\np1=%u",p1);        printf("\nm=%d",m);            getch();     return 0; } 

this gives output as:

p2= 2686792 p1= 1993645620 m= -497739707 

i have 2 doubts code , output:

1. since 'm' int, shouldn't take p2-p1 input since p1 , p2 both pointers , m integer should give error "invalid conversion 'int' 'int' " isn't. why?

2. even after takes input, difference isn't valid. why it?

since 'm' int, shouldn't take p2-p1 input since p1 , p2 both pointers , m integer should give error "invalid conversion 'int' 'int' " isn't. why?

this type of error or warning depends on compiler using. c compilers times give programmers plenty of rope hang with...

even after takes input, difference isn't valid. why it?

actually, difference correct! using pointer arithmetic perform calculation. example..

p2= 2686792

p1= 1993645620

since pointers not initialized, assigned garbage values ones above. now, want perform operation p2 - p1, i.e. asking memory address comes p1 memory blocks before p2. since p1 , p2 pointers integers, size of memory block sizeof(int) (almost 4 bytes). therefore:

p2 - p1 = (2686792 - 1993645620) / sizeof(int) = (2686792 - 1993645620) / 4 = -497739707