c - How exactly pointer subtraction works in case of integer array? -

#include<stdio.h> int main() {     int arr[] = {10, 20, 30, 40, 50, 60};     int *ptr1 = arr;     int *ptr2 = arr + 5;     printf("number of elements between 2 pointer are: %d.",                                  (ptr2 - ptr1));     printf("number of bytes between 2 pointers are: %d",                                 (char*)ptr2 - (char*) ptr1);     return 0; } 

for first printf() statement output 5 according pointer subtraction confusion

what second printf() statement, output?

to quote c11, chapter §6.5.6, additive operators

when 2 pointers subtracted, both shall point elements of same array object, or 1 past last element of array object; result difference of subscripts of 2 array elements.

so, when you're doing

printf("number of elements between 2 pointer are: %d.",                              (ptr2 - ptr1)); 

both ptr1 , ptr2 pointers int, hence giving difference in subscript, 5. in other words, difference of address counted in reference sizeof(<type>).

otoh,

 printf("number of bytes between 2 pointers are: %d",                             (char*)ptr2 - (char*) ptr1); 

both ptr1 , ptr2 casted pointer char, has size of 1 byte. calculation takes place accordingly. result: 20.

fwiw, please note, subtraction of 2 pointers produces result type of ptrdiff_t , should using %td format specifier print result.