SOURCE

//改进： 定义一个变量记录“=”的输入与否而不必每输入数字时都要检索一遍文本框内容

 

 

var status=0;	//标记所输入的是数字还是运算符号

var calcu=0;	//标记所要执行的方法是哪一个

 

 

/*数字、括号及PI的输入*/

function num(x){

	var str0=document.getElementById('result0').value;

	var str=document.getElementById('result').value;

	if(str0.indexOf("=")>0){

		document.getElementById('result0').value='';

		document.getElementById('result').value='0';

		str=document.getElementById('result').value;

	}

	if(str=="0")

		str='';

 	str+=String(x);

 	document.getElementById('result').value=str;

 	status=0;

}

//输入. （未做是否包含“.”的判断）

function dot(){

	var str0=document.getElementById('result0').value;

	var str=document.getElementById('result').value;

	if(str0.indexOf("=")>0){

		document.getElementById('result0').value='';

		document.getElementById('result').value='0';

		str=document.getElementById('result').value;

	}

	str=str+'.';

 	document.getElementById('result').value=str;

}

 

 

/*三角函数以及'1/'计算*/

function sin(){

	calcu=1;

	cal();

}

function cos(){

	calcu=2;

	cal();

}

function tan(){

	calcu=3;

	cal();

}

function divide1(){

	calcu=4;

	cal();

}

function ln(){

	calcu=5;

	cal();

}

function log(){

	calcu=6;

	cal();

}

function cal(){

	var str0=document.getElementById('result0').value;

	var str=document.getElementById('result').value;

	if(str0.indexOf("=")>0){

		document.getElementById('result0').value='';

		document.getElementById('result').value='0';

		str=document.getElementById('result').value;

	}

	if(str=="0")

		str='';

	switch(calcu){                                   

        case 1: str+=String("sin(");break;               

        case 2: str+=String("cos(");break;               

        case 3: str+=String("tan(");break; 

        case 4: str+=String("1/");break;

        case 5: str+=String("ln(");break;

        case 6: str+=String("log(");break;

    }   

 	document.getElementById('result').value=str;

 	status=1;

}

 

 

/*   ^、√以及%的输入   */

function pow1(){

	calcu=1;

	powS();

}

function pow2(){

	calcu=2;

	powS();

}

function quyu(){

	calcu=3;

	powS();

}

function powS(){

	if(status == 1)

		return;

	var strpow0=document.getElementById('result0').value;

	var strpow=document.getElementById('result').value;

	if(strpow0.indexOf("=")>0){

		document.getElementById('result0').value='';

		/*document.getElementById('result').value='0';*/

		strpow=document.getElementById('result').value;

	}

	switch(calcu){

		case 1: strpow+=String('^');

 			    break;

		case 2: if(strpow=='0')

			  		strpow="√";

			  	else{

			  		strpow+=String('√');

			  	}

			    break;

		case 3: strpow+=String("%");

				break;

	}

	document.getElementById('result').value=strpow;

	status=1;

}

 

 

 

 

/*   +-×÷ 运算   */

function plus(){

	calcu=1;

	calculate();

}

function times(){

	calcu=2;

	calculate();

}

function divide(){

	calcu=3;

	calculate();		

}

function calculate(){

	if(status==1)

		return;

	var str0=document.getElementById('result0').value;

	var str=document.getElementById('result').value;

	if(str0.indexOf("=")>0 ){

		document.getElementById('result0').value='';

		/*document.getElementById('result').value='0';*/

		str=document.getElementById('result').value;

	}

	if(str=='')

		str='0';

	switch(calcu){

		case 1: str+='+';break;

		case 2: str+='×';break;

		case 3: str+='÷';break;

	}

 	document.getElementById('result').value=str;

 	status=1;

}

function minus(){

	var str0=document.getElementById('result0').value;

	var str=document.getElementById('result').value;

	if(str0.indexOf("=")>0){

		document.getElementById('result0').value='';

		/*document.getElementById('result').value='-';*/

		str=document.getElementById('result').value+'-';

	}

 	else

 		str+='-';

 	document.getElementById('result').value=str;

}

 

 

//显示屏字符串为空

function zero(){

	document.getElementById('result0').value="";

 	document.getElementById('result').value="0";

}

 

 

//显示屏字符串减去最后一个字符

function back(){

	var str0=document.getElementById('result0').value;

	var str=document.getElementById('result').value;

	if(str0.indexOf("=")>0 || str=='')

		return;

	var str1=str.substr(0,(str.length)-1)

 	document.getElementById('result').value=str1;

}

 

 

//获取当前显示屏字符，判断所包含运算符，并做相关运算。

function equal(){

	var str0=document.getElementById('result').value;

	if(str0=="")

		return;

	var str=str0.replace(/×/g,'*');		//用正则表达式进行全部替换

	str=str.replace(/÷/g,'/');

	str=str.replace(/π/g,'Math.PI');

	if(str.indexOf("sin")>=0){

		str=str.replace(/sin/g,'Math.round(Math.sin');

		str+='*1000000)/1000000';

 

 

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=eval(str);

		

	}

	else if(str.indexOf("cos")>=0){

		str=str.replace(/cos/g,'Math.round(Math.cos');

		str+='*1000000)/1000000';

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=eval(str);

	}

	else if(str.indexOf("tan")>=0){

		str=str.replace(/tan/g,'Math.round(Math.tan');

		str+='*1000000)/1000000';

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=eval(str);

	}

	else if(str.indexOf("^")>=0){

		var pos=str0.indexOf('^');

		var pow1=str0.substring(0,pos);

		var pow2=str0.substring(pos+1,str0.length+1);

		result=Math.pow(pow1, pow2);

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=eval(result);

	}

	else if(str.indexOf("√")>=0){

		var pos=str0.indexOf('√');

		var pow1=str0.substring(0,pos);

		var pow2=str0.substring(pos+1,str0.length+1);

		if(pow1==''){

			result=Math.pow(pow2,0.5);

			document.getElementById('result0').value=str0.concat("=");

			document.getElementById('result').value=eval(result);

		}

		else{

			result=Math.pow(pow2, 1/pow1);

			document.getElementById('result0').value=str0.concat("=");

			document.getElementById('result').value=eval(result);

		}

	}

	else if(str.indexOf("ln")>=0){

		var str=str0.replace(/ln/g,'Math.round(Math.log');

		str+='*1000000)/1000000';

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=eval(str);

	}

	else if(str.indexOf("log")>=0){

		var str=str0.replace(/log/g,'Math.log');

		str+= '/Math.log(10)';

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=eval(str);

	}

	else{

		result=(eval(str));

		document.getElementById('result0').value=str0.concat("=");

		document.getElementById('result').value=result;

	}

	var a=document.getElementById('result').value;

	if(a=="Infinity")

		document.getElementById('result').value='∞';

	else if(a=="-Infinity")

		document.getElementById('result').value='-∞';

}

function styleChange(){

	if(document.getElementById('rows').style.display=='inline'){

		document.getElementById('rows').style.display='none';

		document.getElementById('sci').style.display='inline';

	}

	else if(document.getElementById('rows').style.display=='none'){

		document.getElementById('rows').style.display='inline';

		document.getElementById('sci').style.display='none';

	}

}

<div id="calculator">

	<a href="http://write.blog.csdn.net/postlist" id='record'>计Sweet Smile</a>

	<div class="rescult">

		<textarea type="text" id="result0" onfocus="this.blur();"></textarea>

		<textarea type="text" id="result" onfocus="this.blur();"></textarea>

	</div>

 	<div>

		<section class="model-1">           <!--包含按钮的一个长形区域-->

		  <div class="checkbox"  onclick="styleChange()">			

		  <!--包含按钮的一个较小长形区域-->

		    <input type="checkbox"/>

		    <label>科学标准</label>					<!--按钮底部的灰色滑动区-->

		  </div>

		</section>

	</div>

 

	<!--标准计算器布局-->

 	<div id="rows" style="display:inline;">

	<div class="row1">

		<button id="bt1" onclick="zero()">C</button>

		<button id="bt2" onclick="back()">DEL</button>

		<button id="bt3" onclick="divide()">÷</button>

		<button id="bt4" onclick="times()">×</button>

	</div>

	<div class="row2">

		<button id="bt5" onclick="num(7)">7</button>

		<button id="bt6" onclick="num(8)">8</button>

		<button id="bt7" onclick="num(9)">9</button>

		<button id="bt8" onclick="plus()">+</button>

	</div>

	<div class="row3">

		<button id="bt9" onclick="num(4)">4</button>

		<button id="bt10" onclick="num(5)">5</button>

		<button id="bt11" onclick="num(6)">6</button>

		<button id="bt12" onclick="minus()">-</button>

	</div>

 

	<div id="below">

		<div id="left">

			<div class="row4">

				<button id="bt13" onclick="num(1)">1</button>

				<button id="bt14" onclick="num(2)">2</button>

				<button id="bt15" onclick="num(3)">3</button>

			</div>

			<div class="row5">

				<button id="bt16" onclick="num(0)">0</button>

				<button id="bt17" onclick="dot()">.</button>

			</div>

		</div>

		<div id="right">

			<button id="bt18" onclick="equal()">=</button>

		</div>

	</div>

 

	</div>

 

	<!--科学计算器布局-->

	<div id="sci"  style="display:none;">

		<div class="sci1">

				<button id="bt21" onclick="zero()">C</button>

				<button id="bt22" onclick="back()">DEL</button>

				<button id="bt23" onclick="pow1()">^</button>

				<button id="bt24" onclick="num('π')">π</button>

				<button id="bt25" onclick="pow2()">√</button>

		</div>

		<div class="sci2">

				<button id="bt26" onclick="sin()">sin</button>

				<button id="bt27" onclick="num('(')">(</button>

				<button id="bt28" onclick="num(')')">)</button>

				<button id="bt29" onclick="divide1()">1/X</button>

				<button id="bt30" onclick="divide()">÷</button>

		</div>

		<div class="sci3">

				<button id="bt31" onclick="cos()">cos</button>

				<button id="bt32" onclick="num(7)">7</button>

				<button id="bt33" onclick="num(8)">8</button>

				<button id="bt34" onclick="num(9)">9</button>

				<button id="bt35" onclick="times()">×</button>

		</div>

		<div class="sci4">

				<button id="bt36" onclick="tan()">tan</button>

				<button id="bt37" onclick="num(4)">4</button>

				<button id="bt38" onclick="num(5)">5</button>

				<button id="bt39" onclick="num(6)">6</button>

				<button id="bt40" onclick="minus()">-</button>

		</div>

		<div class="sci5">

				<button id="bt41" onclick="ln()">ln</button>

				<button id="bt42" onclick="num(1)">1</button>

				<button id="bt43" onclick="num(2)">2</button>

				<button id="bt44" onclick="num(3)">3</button>

				<button id="bt45" onclick="plus()">+</button>

		</div>

		<div class="sci6">

				<button id="bt46" onclick="log()">log</button>

				<button id="bt47" onclick="num(0)">0</button>

				<button id="bt48" onclick="dot()">.</button>

				<button id="bt49" onclick="quyu()">%</button>

				<button id="bt50" onclick="equal()">=</button>

		</div>

 

	</div>

 

	

</div>

 

body { 

 

	font-size:24px; 

	font-family:Arial, Georgia, "Times New Roman", Times, serif; 

	color:#555; 	

	text-align:center; 		

	background-color:#555; 		

}

body div{

	align:center;

	margin-top:5px;	

} 

#calculator{

	align:center;

	width:350px;

  height:550px;

	margin:10px auto;

	border:#fff 2px solid;	

	overflow:hidden;      

	background-color:#f2f2f2; 	

 

}

 

.rescult{

	align:center;

	padding:10px 5px 0px 5px;

}

#result,#result0{

	width:300px;

	height:40px;

	font-size:35px;

	text-align:right;

	direction:ltr; 

	border:#C0C0C0;

	overflow:hidden;      

	background-color:#C0C0C0;

	word-wrap : normal;	

}

#result0{

  font-size:25px;

}

section {

  float: left;

  width:100px;

  padding: 0px 200px 10px 20px;

  height: 50px;

}

 

.checkbox {

  position: relative;

  display: inline-block;    

}

 

.checkbox label {

  font-size:20px;

  text-align: center;

  padding-top: 5px;

  width: 90px;

  height: 30px;

  position: relative;

  display: inline-block;

  border-radius: 46px;        

  -webkit-transition: 0.4s;   

  transition: 0.4s;

}

.checkbox label:after {    

  content: '';

  position: absolute;

  padding-top: 20px;

  width: 45px;

  height: 20px;

  border-radius: 40%;

  left: 0;                

  top: -5px;

  z-index: 2;       

  background: #f2f2f2;   

  box-shadow: 0 0 5px rgba(0, 0, 0, 0.2);   

  -webkit-transition: 0.4s;  

  transition: 0.4s;

}

.checkbox input {

  position: absolute;

  left: 0;

  top: 0;

  width: 100%;      

  height: 100%;

  z-index: 5;       

  opacity: 0;      

  cursor: pointer;  

}

 

.checkbox input:hover + label:after {

  box-shadow: 0 2px 15px 0 rgba(0, 0, 0, 0.2), 0 3px 8px 0 rgba(0, 0, 0, 0.2);

}

.checkbox input:checked + label:after {

  left: 45px;