Postfix Evaluator
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/*
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
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));
}
Postfix Evaluator
Postfix Expression :
Result :
This JavaScript evaluates a Postfix(Postorder) expression.
Click here for the algorithm used.
© 2002 Premshree Pillai.