multiple driver error during simulation

--- Quote Start ---

(vhdl clocked process)
--detect edge of switch
switch_d <= switch;
if switch = '1' and switch_d = '0' then
   count <= 1;
elsif count < 8 then
   count <= count + 1;
end if;
if count < 8 then
    output(count) <= input;
end if;
if count = 7 then
    valid <= '1';
else
    valid <= '0';
end if;

--- Quote End ---

As per the specifications the first 8 inputs are to be taken at the positive edge of switch.

So why do you set count =1 at +ve edge and increase it by 1 when there's no posedge of switch?

2)

if count < 8 then output(count) <= input; end if;

what is this used for?