[@abulkhondker3556]

The reason for the undefined (red) value (x) was the synchronous Reset.
always@(posedge clock) begin
if (reset) accumulator

[@amariakader6134]

great course thanks.
I tried to simulate the code but the negative part of sine wave seem to be positive why is that?

[@hunteradams9430]

In the Wave window, do you have the signal Radix set to Decimal (as opposed to Unsigned)? Right click signal name --> Radix --> Decimal. You can see the Radix option at 16:47.

[@amariakader6134]

@@hunteradams9430 thank you sir it worked