Mega Code Archive
Postfix Evaluator
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<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<html>
<head>
<title>Postfix Evaluator</title>
<style type="text/css">
.header{font-family:verdana,arial,helvetica; font-weight:bold; font-size:22pt; color:#0066CC; filter:DropShadow(color=#CCCCFF, offX=2, offY=2, positive=1); width:100%}
.form_in{background:#FFFFFF; border:#0066CC solid 1px}
.text_box{font-weight:bold; background:#EEEEFF; border:#0066CC solid 1px; height:20px}
.button{background:#0066CC; font-weight:bold; color:#FFFFFF; border:#0066CC solid 1px; height:20px; cursor:hand}
.link{color:#0066CC}
.link:hover{color:#0099FF}
</style>
</head>
<body bgcolor="#FFFFFF">
<!--BEGIN POSTFIX EVALUATOR JAVASCRIPT-->
<script language="JavaScript">
/*
Postfix Evaluator
- Evaluates a Postfix(Postorder) expression
- For eg. '12*3+' results in 5
- Valid Operators are +,-,*,/
- No Error Handling in this version
JavaScript Implementation
- CopyRight 2002 Premshree Pillai
See algorithm at
-http://www.qiksearch.com/articles/cs/postfix-evaluation/index.htm
Created : 02/09/02 (dd/mm/yy)
Web : http://www.qiksearch.com
E-mail : qiksearch@rediffmail.com
*/
function push_stack(stackArr,ele)
{
stackArr[stackArr.length]=ele;
}
function pop_stack(stackArr)
{
var _temp=stackArr[stackArr.length-1];
delete stackArr[stackArr.length-1];
stackArr.length--;
return(_temp);
}
function isOperand(who)
{
return(!isOperator(who)? true : false);
}
function isOperator(who)
{
return((who=="+" || who=="-" || who=="*" || who=="/" || who=="(" || who==")")? true : false);
}
function topStack(stackArr)
{
return(stackArr[stackArr.length-1]);
}
function PostfixSubEval(num1,num2,sym)
{
var returnVal;
if(sym=="+")
returnVal=num1+num2;
if(sym=="-")
returnVal=num1-num2;
if(sym=="*")
returnVal=num1*num2;
if(sym=="/")
returnVal=num1/num2;
return(returnVal);
}
function PostfixEval(postfixStr)
{
var stackArr=new Array();
postfixStr=postfixStr.split('');
for(var i=0; i<postfixStr.length; i++)
{
if(isOperand(postfixStr[i]))
{
push_stack(stackArr,postfixStr[i]);
}
else
{
var temp=parseFloat(topStack(stackArr));
pop_stack(stackArr);
var pushVal=PostfixSubEval(parseFloat(topStack(stackArr)),temp,postfixStr[i]);
pop_stack(stackArr);
push_stack(stackArr,pushVal);
}
}
return(topStack(stackArr));
}
</script>
<!--END POSTFIX EVALUATOR JAVASCRIPT-->
<center><span class="header">Postfix Evaluator</span></center>
<!--BEGIN FORM-->
<center>
<form name="input_form">
<table class="form_in" cellspacing="0" cellpadding="3">
<tr bgcolor="#0066CC">
<td><font face="verdana,arial,helvetica" size="-2" color="#FFFFFF">Postfix Expression :</font></td>
<td><font face="verdana,arial,helvetica" size="-2" color="#FFFFFF">Result :</font></td>
<td></td>
</tr>
<tr>
<td><input type="text" name="postfixVal" class="text_box" value=""></td>
<td><input type="text" name="resultVal" class="text_box" value=""></td>
<td align="bottom"><input type="button" onClick="document.input_form.resultVal.value=PostfixEval(document.input_form.postfixVal.value)" value="Evaluate Postfix" class="button"></td>
</tr>
</table>
</form>
</center>
<!--END FORM-->
<table width="485" align="center"><tr><td>
<font face="verdana,arial,helvetica" size="-1" color="#000000">
This JavaScript evaluates a Postfix(Postorder) expression.
<br><br><a href="http://www.qiksearch.com/articles/cs/postfix-evaluation/index.htm" class="link">Click here</a> for the algorithm used.
<hr style="color:#003366; height:1px">
© 2002 <a href="http://www.qiksearch.com" class="link" title="Click here to visit Qiksearch.com">Premshree Pillai</a>.
</font>
</td></tr></table>
</body>
</html>
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