How to hardcode variable values ​​in C at compile time?

Question

C++ / C#

For example, there is such code
int main()
{
//int a = ?
//int b = ?
asm("add r10, %0, %1", : :"r"(a), "r"(b));
return 0;
}
How to set variables a and b as numbers at compile time?

Answer 1

All found gcc -Da=10 -Db=12

Answer 2

Through preprocessor directives. #define and all that. And by the way, as far as I know, it's right to hardcode.