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简单计算（100一内的加减乘除计算功能）简单易懂

#include <reg52.h>                   //包含文件
#define uchar unsigned char
#define uint  unsigned int

char b[]={0xc0,0xf9,0xa4,0xb0,0x99,0x92,0x82,0xf8,0x80,0x90,0x88,0x83,0xc6,
		  0xa1,0x86,0x8e,0x8c,0xc1,0xce,0x91,0x89,0xc7,0xff};    // 共阴极字符码

//延时函数，用于实现程序中的短暂延时，表示延时cnt个毫秒
void delay(unsigned int cnt)
{
	unsigned char i;
	while(cnt--)
	{
		for(i=220;i>0;i--)
		;
	}
}

//键盘扫描程序
uchar keyboardscan(void) 
{
	  uchar sccode,recode;
	  P1=0xf0;    //P1口附初值
	  if((P1&0xf0)!=0xf0)//如果P1口电平不等于0xf0，表示有按键按下
	  { 
	      delay(20);    //延时20毫秒后再判断，看是否还有按键按下，次步为软件防抖
	      if((P1&0xf0)!=0xf0)//继续判断是否有按键按下
	     { 
	          sccode=0xfe;  //进行逐行判断
	          while((sccode&0x10)!=0)
	         { 
			      P1=sccode;
	        	  if((P1&0xf0)!=0xf0)
	              {
			 		  recode=(P1&0xf0|0x0f);
			 		  switch((~sccode)+(~recode))
			          {   // 下面是键盘的编码识别
				          case 0x11:	return(1);    break;
				          case 0x21:  return(2);    break;
				          case 0x41:	return(3);	   break;
				          case 0x81:	return(11);  break;//返回对应的键值0~15
				          case 0x12:	return(4);    break;
				          case 0x22:  return(5);    break;
				          case 0x42:  return(6);    break;
				          case 0x82:	return(12);	  break;
				          case 0x14:	return(7);    break;
				          case 0x24:  return(8);	break;
				          case 0x44:  return(9);   break;
				          case 0x84:	return(13);  break;
				          case 0x18:	return(10);   break;
				          case 0x28:	return(15);   break;
				          case 0x48:  return(16);   break;
				          case 0x88:	return(14);  break;
						  default:break;
			 }
	        }
	        else 
	            sccode = (sccode<<1)|0x01;
	      }
	    }
	  }
	 return(0xff); //如果没有按键按下，则返回0xff
}
void output(uchar number)
{
P0=b[number/10];
P2=b[number%10];
}
int yunsuan(uchar a,uchar b,uchar c)
{
	switch(c)
	{
		case 1:return(a/b);break;
		case 2:return(a*b);break;
		case 3:return(a-b);break;
		case 4:return(a+b);break;
	}
}
void main(void)	                //主函数 
{ 
	unsigned char n1,n2,key,index,a;
	n1=n2=index=0;
	P0=P2=b[0];
	while(1)
	{
		key = keyboardscan();//键盘扫描，看是否有按键按下
		if(key != 0xff)//如果有按键按下，则key不再是0xff了，显示该按键键值
		{
			if(key<10)
			{
				if(!index) n1=key%10;
				else n2=key%10;
				output(key%10);
			}
			else if(key==15)
			{
				n1=n2=index=0;
				output(0);
			}
			else if(key==16)
			{
				if(!index) output(n1);
				else
				{
					a=yunsuan(n1,n2,index);
					a=a%100;
					output(a);
					n1=a;
					n2=index=0;
				}
			}
			else
			{		
				if(index==0||n2==0) index=key-10;
				else
				{
					a=yunsuan(n1,n2,index);
					a=a%100;
					output(a);
					n1=a;
					n2=0;
					index=key-10;
				}
			}
		}
	}
}