structure

[Raja ali]

#include<stdio.h>
#include<conio.h>
#include<string.h>
struct 
{
    int num1,num2;
    char s1;
    int *ptr;
    int abc[5];
}a[2];

void main()

 {
     int start, last;
     start=&a[1].num1;//error
     last=&a[0].num1;//error
     printf("\nsize of structure :%d bytes",start-last);
     getch();
     }


    getch();
}

[Raja ali]

please correct error in 16 and 17 lines

[Ancient Dragon]

remove the & address symbol from both those lines

[nullptr]

Seeing as start and last are both int, you just need to cast &a[1].num1 and &a[0].num1 as type int.
start = (int) &a[1].num1;
Or quite simply you could use:
printf("\nsize of structure :%d bytes", sizeof(a[0]) );