Am I too stupid for programming?

I wrote a C compiler but I don't think I'm smart enough to do anything much serious. Never learnt C++. Did learn Java, OCaml, and C#. How can I know if I'm too stupid for programming? It seems so complex

Doing something "serious" takes time, more than skill. The vast majority of programming you need to do for a practical large-scale project is tedious bullshit. It's just about if you have enough patience or autism to suffer through that for a long time (months to years) without your interest waning until you have something worthwhile.