JS实现可针对算术表达式求值的计算器功能示例

/* CSS Document */
body
{
 /*  padding-right:40%;
   padding-left:40%;*/
   text-align:center;
}
div{
  background-color:orange;
  height:300px;
  width:300px;
  margin-left:auto;
  margin-right:auto;
  margin-bottom:auto;
  margin-top:50px;
  border-style: groove;
  border-color: Green;
/*  margin-top:auto;*/
}
#in{
    position:relative;
    margin-left:20px;
    margin-top:10px;
    height:27px;
    width:260px;
    background:red;
    top:40px
  }
.clsin
  {
    height:27px;
    width:200px;
    background-color:#FFF;
  }
#num{
    position:relative;
    margin-left:20px;
    margin-top:45px;
    height:150px;
    width:250px;
    background-color:green;
    text-align:left;
  }
#num input
  {
    margin-right:10px;
    margin-top:10px;
    width:35px;
  }

str_exp=""; //存放表达式
function test(obj)   //数字 运算符 btn  click
{
    str_exp+=obj.value;
    document.getElementById("input").value=str_exp;
}
function compare( ch2, ch3)         //比较运算符ch2和ch3优先级
{
  array1=new Array('+','-','*','/','(',')','@');
  array20=new Array('>','>','<','<','<','>', '>');
  array21=new Array( '>','>','<','<','<','>','>');
  array22=new Array( '>','>','>','>','<','>','>');
  array23=new Array('>','>','>','>','<','>','>');
  array24=new Array('<','<','<','<','<','=',' ');
  array25=new Array('>','>','>','>',' ','>','>');
  array26=new Array( '<','<','<','<','<',' ','=');
  array2=new Array(array20,array21,array22,array23,array24,array25,array26);
//  b[7][7]={'>','>','<','<','<','>','>',  // +
//        '>','>','<','<','<','>','>',   // -
//        '>','>','>','>','<','>','>',   // *
//        '>','>','>','>','<','>','>',   // /
//        '<','<','<','<','<','=',' ',   // (
//         '>','>','>','>',' ','>','>',  // )
//         '<','<','<','<','<',' ','=' }; // @
  for(var i=0;ch2!=array1[i];i++);
  for(var j=0;ch3!=array1[j];j++);
  return array2[i][j];
}
function operate(a,preop,b)  //计算a？b的值
{
 // var num1=parseInt(a,10);
 // var num2=parseInt(b,10);
  var num1=parseFloat(a);
  var num2=parseFloat(b);
//  alert("a:"+num1+preop+"b:"+num2);
  switch(preop)
  {
  case'+':return(num1+num2);break;
  case'-':return(num1-num2);break;
  case'*':return(num1*num2);break;
  case'/':return(num1/num2);break;
//  default: cout<<"erro"<0)
   {
   expPre=str2.charAt(i-1); ///////////////////////!!
   if(isNum(expTemp)&&isNum(expPre))  //判断前后连续取到的是否都是数字字符，是则拼接
   {
    str_temp[j-1]+=expTemp;
    j--;
   }
    else
    {
     str_temp[j]=expTemp;
    }
   }
   j++;
 }
 return str_temp;
}
function exp_result()
{
  str_exp=str_exp+'@';
  str=divided(str_exp);
  numArray=new Array();  //存放操作数
  symbolArray =new Array();//存放操作符
  symbolArray.push('@');
 //  numArray.push('@');
// alert(str.length);
  for(var i=0;str[i]!='@'||symbolArray[symbolArray.length-1]!='@';i++)
  {
//    alert(str[i]);
//    alert(symbolArray[symbolArray.length-1]);
    if(isNum(str[i]))
    {
 //     alert("Num push:"+str[i]);
     numArray.push(str[i]);
    }
    else
    {
 //    alert("symbol:"+str[i]);
    preop=symbolArray[symbolArray.length-1];  //取栈顶元素
    switch(compare(preop,str[i]))
    {
      case'<':symbolArray.push(str[i]);break;
      case'=':symbolArray.pop();break;
      case'>':b=numArray.pop();a=numArray.pop();preop=symbolArray.pop(); //取两操作数与之前操作符运算
          numArray.push(operate(a,preop,b)); //计算结果入栈
         // str.push(str[i]); //当前操作符入栈
          i--;   //继续与之前的操作符比较
          break;
    }
    }
  }
  if(isNaN(numArray[0]))
  {
   alert("算术表达式输入有误!!");
  }
  else
  alert("结果为："+numArray[0]);
  str_exp="";
  document.getElementById("input").value=str_exp;
}