How is this number calculated?

Question

I have numbers;

A == 0x20000000
B == 18
C == (B/10)
D == 0x20000004 == (A + C)

A and D are in hex, but I'm not sure what the assumed numeric bases of the others are (although I'd assume base 10 since they don't explicitly state a base.

It may or may not be relevant but I'm dealing with memory addresses, A and D are pointers.

The part I'm failing to understand is how 18/10 gives me 0x4.

Edit: Code for clarity:

*address1 (pointer is to address: 0x20000000)

printf("Test1: %p\n", address1);
printf("Test2: %p\n", address1+(18/10));
printf("Test3: %p\n", address1+(21/10));

Output:

Test1: 0x20000000
Test2: 0x20000004
Test3: 0x20000008