Hi everyone,
today we will learn how to use seven segment display and usage of case-when. 
At my one of the earlier post i did counter but now i improved the program. 
Now it counts from "0000" to "1001" then it goes back.

I have a reset input as you see and at the end of the program there are two when-case 
situation. These are fır the seven segment displays at Cyclone V SoC 5CSEMA5F31 board.

library ieee;
use ieee.std_logic_1164.all;
use IEEE.STD_LOGIC_ARITH.ALL;
use ieee.std_logic_unsigned.all;

entity BCD_counter is
generic (N : integer:= 3 );
port( clk : in std_logic;
rst : in std_logic;
y   : out std_logic_vector(3 downto 0) );
end entity;

architecture behavioral of BCD_counter is

signal ara : std_logic_vector(3 downto 0);

begin

process(clk,rst)

begin
if rst = '1' then
ara <= "0000";
--    elsif ara = "1010" then
--    ara <= "0000";
elsif rising_edge(clk) then
ara <= ara + "0001" ;
else
ara <= ara;
end if;
end process;
y <= ara;
process(y)
begin
case y(3 downto 0) is
when "0000" => segment1 <= "1000000";
when "0001" => segment1 <= "1001111";
when "0010" => segment1 <= "0100100";
when "0011" => segment1 <= "0110000";
when "0100" => segment1 <= "0011001";
when "0101" => segment1 <= "0100100";
when "0110" => segment1 <= "0000010";
when "0111" => segment1 <= "0111000";
when "1000" => segment1 <= "0000000";
when "1001" => segment1 <= "0011000";
when "1010" => segment1 <= "0100000";
when "1011" => segment1 <= "0000011";
when "1100" => segment1 <= "1000110";
when "1101" => segment1 <= "0100001";
when "1110" => segment1 <= "0000110";
when others => segment1 <= "0001110";
end case;

case y(7 downto 4) is
when "0000" => segment2 <= "1000000";
when "0001" => segment2 <= "1001111";
when "0010" => segment2 <= "0100100";
when "0011" => segment2 <= "0110000";
when "0100" => segment2 <= "0011001";
when "0101" => segment2 <= "0100100";
when "0110" => segment2 <= "0000010";
when "0111" => segment2 <= "0111000";
when "1000" => segment2 <= "0000000";
when "1001" => segment2 <= "0011000";
when "1010" => segment2 <= "0100000";
when "1011" => segment2 <= "0000011";
when "1100" => segment2 <= "1000110";
when "1101" => segment2 <= "0100001";
when "1110" => segment2 <= "0000110";
when others => segment2 <= "0001110";
end case;

end process;
end behavioral;
--ozturkgokhan.com

Modelsim Output

best wishes,
gökhan öztürk