Can hexadecimal numbers be added/subtracted with decimal numbers?

Question

When programming in C, say if I have integer h as a hexadecimal value and integer d as a decimal number. Can I do addition or subtraction between h and d? Or do they have have to be in the same number system?

Answer 1

Yes, you can write:

int x = 100 - 0x100 + 0100;

That mixes decimal with hex and octal. The values are all converted to binary anyway before the calculation occurs (and the compiler will do the calculation in this example; it won't be evaluated at runtime). And any of the constants can be replaced by an int value that was assigned the appropriate value:

int d = 100;
int h = 0x100;
int o = 0100;
int x = d + h + o;

Answer 2

Yes they can, for example

int x;
x = 0x0F + 10;
printf("%d\n", x);

Output:

25

the representation you use doesn't matter, it will be ultimately all converted to binary after all.