Help with reseting counet

Entity VCO is

Port(sw:in std_logic;

Clk:in std_logic;

Bit_4: out std_logic_vectot(3 downto 0));

End entity;

Architecture behave of VCO is

Signal cnt: integer range 0 to 50000000:=0;

Signal f_out: std_logic_vector(3 downto 0):=x"0";

Begin

Process (clk)

Begin

If sw = '1' then

If clk 'event and clk=' 1' then

Cnt<=cnt+1;

If cnt=5 then

F_Out<=f_out+'1';

Cnt<=0;

Elsif cnt=5 then

If f_out="1111" then

F_out<="1111"

Cnt<=0;

End if;

End if;

End if;

Elsif ='0' then

Cnt<=0;

F_out<="ZZZZ";

End if;

End process;

Bit_4<=f_out;

End;