数码管显示的密码锁设计；为什么按一个键没用不显示数字，按了两个键才显示数字。C51单片机

#include<reg51.h>char scan_key(void);void delay(unsigned int i);sbit P30=P3^0;void main(){unsigned char led[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,0xa1,0x86,0x8e};unsigned char led1[]={0xbf,0x8c,0x86};unsigned char i;P1=led1[0];P30=1;P0=0xff;while(1){i=scan_key();if(i==-1)continue;else if(i!=8){P1=led[i];delay(1000);P1=led1[2];delay(2000);P1=led1[0];}else{P1=led[i];delay(1000);P1=led1[1];P30=0;delay(2000);P1=led1[0];P30=1;}}}char scan_key(){char i,temp,m,n;bit find=0;P0=0xf0;i=P2;i&=0x0f;if(i!=0x0f){delay(4);i=P2;i&=0x0f;if(i!=0x0f){for(i=0;i<4;i++){P0=0xfe<<i;temp=~P2;temp=temp&0x0f;if(temp!=0x00){n=i;find=1;switch(temp){case 0x01:m=0;break; case 0x02:m=1;break;case 0x04:m=2;break;case 0x08:m=3;break;default:break;}break;}}}}if(find==0)return-1;else return(n*4+m);}void delay(unsigned int i){unsigned int k,j;for(j=0;j<i;j++)for(k=0;k<120;k++);}

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