Cにおけるポインタ(インクリメント、減算、加算、減算)

#include <stdio.h>
int main (void)
{
    int urn[5] = {100,200,300,400,500};
    int *ptr1,*ptr2,*ptr3;
    ptr1 = urn;//         
    ptr2 = &urn[2];//  
                    //        
                    //         
    printf("pointer value,dereferenced pointer,pointer address:
");
    printf("ptr1 = %p,*ptr1 = %d,&ptr1 = %p
",ptr1,*ptr1,&ptr1);
    //    
    ptr3 = ptr1 + 4;
    printf("
adding an int to a pointer:
");
    printf("ptrl + 4 = %p, *(ptr1 + 3) = %d
",ptr1 + 4,*(ptr1+3));
    ptr1++;//    
    printf("
values after ptrl++
");
    printf("ptrl = %p, *ptrl = %d, &ptrl1 = %p
",ptr1,*ptr1,&ptr1);
    ptr2--;//    
    printf("
 values after --ptr2
");
    printf("ptr2 = %p,*ptr2 = %d,&ptr2 = %p
",ptr2,*ptr2,&ptr2);
    --ptr1;//      
    ++ptr2;//  
    //           
    printf("
Pointers reset to original values:
");
    printf("ptr2 = %p,ptrl = %p,ptr2-ptr1 = %d
",ptr2,ptr1,ptr2-ptr1);
    //          
    printf("
subtracting an int from a pointer:
");
    printf("ptr3 = %p,potr3 - 2 = %p
",ptr3,ptr3 - 2);
    return 0;
}