VERILOG 键盘扫码，有几个warning很难解决

使用PMOD键盘，扫描并且在七段数码管显示，综合正确，但是下载后结果不对，可能与几个warnings 有关系，但是我不懂如何消除 。求大神指导
module keyscan(clk,
                        rst_n,
                   keyscan,
              keyin,
              real_number);/////////////////////////////////////////////////////////////////////////////////
  input clk,rst_n;
  input[3:0] keyin;
  output[3:0] keyscan;
  output reg[4:0] real_number;
  reg[3:0] state;
  reg[3:0] four_state;
  reg anykeypress;
  reg[4:0] numberout,number_reg,number_reg1;//
  reg[3:0] scancode;
  reg[3:0] scan_state;
  assign keyscan = scancode;
always@(posedge clk or posedge rst_n)  // part 1 ：  状态机，确定是哪一行数据
if(rst_n)
        begin
          scancode (without init value) has a constant value of 0 in block . This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch (without init value) has a constant value of 0 in block . This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch (without init value) has a constant value of 0 in block . This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:1895 - Due to other FF/Latch trimming, FF/Latch (without init value) has a constant value of 0 in block . This FF/Latch will be trimmed during the optimization process.
WARNING:Xst:2404 -  FFs/Latches > (without init value) have a constant value of 0 in block .     //// 为啥会是恒定0?  搞死人了
WARNING:Xst:2404 -  FFs/Latches > (without init value) have a constant value of 0 in block .
WARNING:Xst:2404 -  FFs/Latches > (without init value) have a constant value of 0 in block .
WARNING:Xst:2404 -  FFs/Latches > (without init value) have a constant value of 0 in block .

求助啊

这个应该是没有设置初始值，后面用了并且赋值了的话就没问题。