Stupid question

I really don't think you mean quite that. Maybe if the assignments were blocking, instead? (always assuming you're trying to do the whole thing in one clock cycle)

This sounds a bit nicer... it depends on the fact that XORing with zero has no effect. Some details missing, of course.

reg [20:0] C; reg [10:0] A, B; integer i; ... C = 0; for (i=0; i

If you just want to avoid the manual replication in the concatenated vector, use the replicate {{ }}:

C[10:0] begin