Firstly, there is no space between the closing bracket at the end of FOR(x,n) and preceding the rest. That's a stylistic concern, but badly hurts readability.

Second, and more significantly, typeof() is not a standard function or operator in C++. It is an extension specific to g++ (GNU c++) in which typeof(x) expands to be type of x and will trigger a compiler error with every compiler that does not support that extension. Within a for loop (assuming you're using g++), if x is an int, then FOR(x,n) would expand to for (int; x < n; x++) which is invalid code.