title: How to remove VHDL type mismatch error due to std_ulogic type does not match integer literal?
body: <p>My goal is to produce a switch track for controlling the <code>position_track</code> and <code>color_track</code> for <code>player1</code> (9-bits) and <code>player2</code> (9-bits) for the board display in a VHDL-based Tic-Tac-Toe game.</p>
  
  <p>Currently, I'm able to display the 3x3 grid and show the color for the switches. Only for <code>player1</code> ('Blue') which is assigned to <code>SW[9]</code> to <code>SW[0]</code> in the Altera DE2 board. <code>player2</code> ('Red') is not responsive in the VGA display for any of the <code>SW[17]</code> to <code>SW[9]</code>.</p>
  
  <p>This is for a project using VHDL with the Altera DE2 board, Cyclone II chip. In the past, I have attempted to check the syntax for entity an architecture (behavioral method) to specify the logic for tracking changes in the built-in hardware switches in the FPGA board.</p>
  
  <p>Used standard libraries such as ieee.std_logic_1164.all and ieee_std.logic_unsigned.all. </p>
  
  <p>FPGA</p>
  
  <pre><code>architecture behavioral of switch_track is
  begin
      process
      begin
          if (player1(0) = '1') then
              position_track(0) &lt;= 1; -- error occurs in this line (19) --
              color_track(0) &lt;= 1;
          elsif
          -- [same logic applies for player2(0)]
          else
              position_track(0) &lt;= 0;
              color_track(0) &lt;= 0;
          end if;
      end process;
  end architecture behavioral;
  
  </code></pre>
  
  <p>I expected that the code in the .vhd file could be synthesized correctly. However, the only error encountered in the Quartus II compiler is:</p>
  
  <blockquote>
    <p>Error (10517): VHDL type mismatch error at switch_track.vhd(19):
    std_ulogic type does not match integer literal.</p>
  </blockquote>
  
  <p>I'm not sure why <code>std_ulogic</code> shows up in the compiler. I'm new to VHDL and Quartus II hardware design. Constructive feedback is appreciated.</p>