要求如下：在没有键摁下的情况下，数码管没有显示。但是每摁下一个键后，会在六个数码上同时显示相同的数字，释放是数码管灭掉。
 
下面是我写的一个程序，运行的结果不对，没键摁下是数码管也有显示，键被摁下之后被释放，数码管依然有显示，这个问题要怎么解决呀？进主函数我就把数码管的位选全部关掉了，结果数码管是乱码，怎么回事？？？求高手解决，怎么改动这个程序
 
#include<reg52.h>
 #define uchar unsigned char
 #define uint  unsigned int
 sbit wela=P2^7;
 sbit dula=P2^6;
 uchar code table[]=
 {0x3f,0x06,0x5b,0x4f,
 0x66,0x6d,0x7d,0x07,
 0x7f,0x6f,0x77,0x7c,
 0x39,0x5e,0x79,0x71};
 uchar temp,num;
 
uchar keyscan();
 void display(uchar aa);
 void delay(uint z);
 
//主函数
 void main()
 {
 
        wela=1;
         P0=0xc0;    //开所有位选
         wela=0;
 
        dula=1;
         P0=0x00;
         dula=0;
 
        while(1)
                 {
                         display(keyscan());
                 }        
}
 //延时函数
 void delay(uint z)
 {
         uint x,y;
         for(x=z;x>0;x--)
                 for(y=110;y>0;y--);
 }
 //键盘扫描函数
 uchar keyscan()
 {
                         P3=0xfe;
                         temp=P3;
                         temp=temp&0xf0;
                         if(temp!=0xf0)
                                 {
                                         delay(8);                   //去抖
                                         temp=P3;
                                         temp=temp&0xf0;
                                         if(temp!=0xf0)
                                                 {
                                                         temp=P3;
                                                         switch(temp)
                                                                 {
                                                                         case 0xee:num=0;break;
                                                                         case 0xde:num=1;break;
                                                                         case 0xbe:num=2;break;
                                                                         case 0x7e:num=3;break;        
                                                                }
                                                 }
                                 }
 
                        P3=0xfd;
                         temp=P3;
                         temp=temp&0xf0;
                         if(temp!=0xf0)
                                 {
                                         delay(8);                   //去抖
                                         temp=P3;
                                         temp=temp&0xf0;
                                         if(temp!=0xf0)
                                                 {
                                                         temp=P3;
                                                         switch(temp)
                                                                 {
                                                                         case 0xed:num=4;break;
                                                                         case 0xdd:num=5;break;
                                                                         case 0xbd:num=6;break;
                                                                         case 0x7d:num=7;break;        
                                                                }
                                                 }
                                 }
 
                        P3=0xfb;
                         temp=P3;
                         temp=temp&0xf0;
                         if(temp!=0xf0)
                                 {
                                         delay(8);                   //去抖
                                         temp=P3;
                                         temp=temp&0xf0;
                                         if(temp!=0xf0)
                                                 {
                                                         temp=P3;
                                                         switch(temp)
                                                                 {
                                                                         case 0xeb:num=8;break;
                                                                         case 0xdb:num=9;break;
                                                                         case 0xbb:num=10;break;
                                                                         case 0x7b:num=11;break;        
                                                                }
                                                 }
                                 }
 
                        P3=0xf7;
                         temp=P3;
                         temp=temp&0xf0;
                         if(temp!=0xf0)
                                 {
                                         delay(8);                   //去抖
                                         temp=P3;
                                         temp=temp&0xf0;
                                         if(temp!=0xf0)
                                                 {
                                                         temp=P3;
                                                         switch(temp)
                                                                 {
                                                                         case 0xe7:num=12;break;
                                                                         case 0xd7:num=13;break;
                                                                         case 0xb7:num=14;break;
                                                                         case 0x77:num=15;break;        
                                                                }
                                                 }
                                 }
         return num;        
}
 
//数码管显示函数
 void display(uchar aa)
 {
                 dula=1;
                 P0=table[aa];
                 dula=0;        
}