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HTML

              
                <head>
 <meta name="viewport" content="width=device-width, initial-scale=1, maximum-scale=1, user-scalable=no">
</head>

<div class="container-fluid" style="zoom:100%;" #id="calculator">
  <div class="calc-screen-area">
    <textarea class="calc-screen" id="calc-screen"></textarea>
  </div>
  <div class="calc-pad">
    <a href="#" class="btn calc-btn-small cal-btn-orange disabled" style="font-size:8px; line-height:22px;">SHIFT</a>
    <a href="#" class="btn calc-btn-small disabled" style="font-size:9px; line-height:22px;">OPTN</a>
    <a href="#" class="btn calc-btn-small disabled" style="font-size:9px; line-height:22px;">VARS</a>
    <a href="#" class="btn calc-btn-small disabled" style="font-size:9px; line-height:22px;">MENU</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall">Ans</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall cal-btn-red" ccmd="FIT">FIT</a>
    <BR>
    <a href="#" class="btn calc-btn-small cal-btn-red disabled " style="font-size:8px; line-height:22px;">ALPHA</a>
    <a href="#" class="btn calc-btn-small" ccmd="SQUARED">𝑥<sup style="font-size:9px;">2</sup></a>
    <a href="#" class="btn calc-btn-small" style="font-size:20px; line-height:25px;" ccmd="POWER">^</a>
    <a href="#" class="btn calc-btn-small" style="font-size:10px; line-height:21px;">EXIT</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall"> </a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall" id="info-icon" data-toggle="modal" data-target="#infoModal">INFO </a>
    <br>
    <a href="#" class="btn calc-btn-small disabled" style="font-size:10px; line-height:21px;">X,T</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall">log</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall">ln</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall">sin</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall">cos</a>
    <a href="#" class="btn calc-btn-small calc-btn-small-textsmall">tan</a>
    <br>
      <a href="#" class="btn calc-btn-small disabled">a<sup>c</sup>/<sub>u</sub></a>
    <a href="#" class="btn calc-btn-small disabled" style="font-size:10px; line-height:21px;">F/D</a>
    <a href="#" class="btn calc-btn-small">(</a>
    <a href="#" class="btn calc-btn-small">)</a>
    <a href="#" class="btn calc-btn-small disabled" style="line-height:13px">,</a>
    <a href="#" class="btn calc-btn-small disabled">➡</a>
    <br>
    <div style="margin:2px; font-size:1px; line-height:2px;"> &nbsp</div>
      
    <div class="calc-btn-top-markings">
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">M</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">N</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">O</span>
      <span class="calc-btn-alt-center">INS</span>
      <span class="calc-btn-alt-center">OFF</span>
    </div>
    <a href="#" class="btn calc-btn">7</a>
    <a href="#" class="btn calc-btn">8</a>
    <a href="#" class="btn calc-btn">9</a>
    <a href="#" class="btn calc-btn cal-btn-grey calc-btn-textsmall" ccmd="DEL" >DEL</a>
    <a href="#" class="btn calc-btn cal-btn-grey" style="font-size: 16px" ccmd="AC">AC<sup style="font-size: 9px; vertical-align:middle;">/ON</sup></a>

    <div class="calc-btn-top-markings">
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">P</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">Q</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">R</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">S</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">T</span>
    </div>
    <a href="#" class="btn calc-btn">4</a>
    <a href="#" class="btn calc-btn">5</a>
    <a href="#" class="btn calc-btn">6</a>
    <a href="#" class="btn calc-btn" style="line-height:27px" ccmd="MULTIPLY">×</a>
    <a href="#" class="btn calc-btn" style="line-height:27px" ccmd="DIVIDE">÷</a>
    
    <div class="calc-btn-top-markings">
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">U</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">V</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">W</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">X</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">Y</span>
    </div>
    <a href="#" class="btn calc-btn">1</a>
    <a href="#" class="btn calc-btn">2</a>
    <a href="#" class="btn calc-btn">3</a>
    <a href="#" class="btn calc-btn" style="line-height:27px" ccmd="ADD">+</a>
    <a href="#" class="btn calc-btn" style="line-height:27px" ccmd="MINUS">−</a>

    <div class="calc-btn-top-markings">
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right">Z</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right"> </span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right"> </span>
      <span class="calc-btn-alt-center">Ans</span>
      <span class="calc-btn-alt-left"> </span><span class="calc-btn-alt-right"> </span>
    </div>
    <a href="#" class="btn calc-btn" lcmd="" ccmd="" rcmd="">0</a>
    <a href="#" class="btn calc-btn" lcmd="" ccmd="DECIMAL POINT" rcmd="" style="line-height:27px">·</a>
    <a class="btn calc-btn calc-btn-textsmall" ccmd="EXPONENT">EXP</a>
    <a class="btn calc-btn calc-btn-textsmall" style="line-height:27px" ccmd="UNERY NEGATIVE">(−)</a>
    <a class="btn calc-btn calc-btn-textsmall cal-btn-purple" ccmd="EXECUTE">EXE</a>
  </div>
 </div>
  
  <!-- Info Modal  -->
<div class="modal fade" id="infoModal" tabindex="-1" role="dialog" aria-labelledby="myinfoLabel">
  <div class="modal-dialog" role="document">
    <div class="modal-content">
      <div class="modal-header">
        <button type="button" id="closeModalCross" class="close" data-dismiss="modal" aria-label="Close"><span aria-hidden="true">&times;</span></button>
        <span class="modal-title" id="myModalLabel"><i class="fa fa-info-circle fa-lg"></i> Calculator</span>
      </div>
      <div class="modal-body">
				<a href="https://codepen.io/sscchan/full/EPNRxq/" target="_blank">
View Portfolio</a>
				<br><br>
				
				<b>Info:</b><br>
        This pen is created as part of FreeCodeCamp's "Build a Javascript Calculator" exercise.  Since there are no Android emulator for the Casio fx-9860, this pen aims to recreate part of the basic calculation function of that calculator so it can be used on an Android phone (or other devices). It is designed to fulfill the following user stories:
<br>        
				<ol>
  <li>I can add, subtract, multiply and divide two numbers.</li>
  <li>I can clear the input field with a clear button.</li>
  <li>I can keep chaining mathematical operations together until I hit the equal button, and the calculator will tell me the correct output.</li>
				</ol>
				
      </div>
    </div>
  </div>
</div>
</body>
              
            
!

CSS

              
                body {
  background-color: #fff;
}

.calculator {
  margin-left: auto;
  margin-right: auto;
}

.calc-screen-area {
  border-radius: 10px 10px 7px 7px;
  background-color: rgb(49, 59, 95);
  padding: 15px 10px 10px 10px;
  width: 288px;
  margin-left: auto;
  margin-right: auto;
}

.calc-screen {
  width: 268px;
  height: 152px;
  border: solid;
  border-width: 14px;
  border-color: rgb(221, 231, 240);
  border-radius: 6px;
  background-color: #fff;
  font-family: 'VT323';
  font-size: 22px;
  line-height: 20px;
}

.calc-pad {
  background-color: rgb(211, 215, 218);
  text-align: center;
  vertical-align: middle;
  width: 280px;
  padding: 5px 0px 15px 0px;
  border-radius: 0px 0px 14px 14px;
  margin: 0px 4px 0px 4px;
  margin-left: auto;
  margin-right: auto;
}

.calc-btn-top-markings {
  height: 13px;
  line-height: 16px;
  padding: 0px;
  margin: 0px 2px 0px 2px;
  font-size: 10px;
}

.calc-btn-alt-left {
  display: inline-block;
  width: 23px;
  margin: 0px 0px 0px 2px;
  padding: 0px 1px 0px 4px;
  text-align: left;
  color: rgb(158, 152, 55);
  font-weight: bold;
}

.calc-btn-alt-right {
  display: inline-block;
  width: 23px;
  margin: 0px 2px 0px 0px;
  padding: 0px 0px 0px 1px;
  text-align: right;
  color: rgb(175, 90, 119);
  font-weight: bold;
}

.calc-btn-alt-center {
  display: inline-block;
  width: 45px;
  margin: 0px 2px 0px 2px;
  padding: 0px;
  text-align: center;
  color: rgb(158, 152, 55);
  font-weight: bold;
}

.calc-btn {
  color: #fff;
  font-family: "verdana";
  text-align: center;
  background-color: rgb(66, 72, 104);
  width: 45px;
  height: 31px;
  border-radius: 8px 8px 11px 11px;
  line-height: 28px;
  padding: 0px;
  margin: 0px 2px 0px 2px;
  font-size: 22px;
  z-index: 0;
  box-shadow: 3px 3px 5px #888888;
}

.calc-btn:visited,
.calc-btn:hover,
.calc-btn:active {
  color: white !important;
}

.calc-btn-textsmall {
  font-size: 16px;
}

.calc-btn-small {
  color: #fff;
  font-family: "verdana";
  text-align: center;
  background-color: rgb(66, 72, 104);
  width: 36px;
  height: 23px;
  border-radius: 8px 8px 10px 10px;
  line-height: 20px;
  padding: 0px;
  margin: 11.5px 2.1px 0px 2.1px;
  font-size: 14px;
  box-shadow: 2px 2px 5px #888888;
}

.calc-btn-small:visited,
.calc-btn-small:hover,
.calc-btn-small:active {
  color: white !important;
}

.calc-btn-small-textsmall {
  font-size: 12px;
}

.calc-btn-small-top-markings {
  height: 11.5px;
  line-height: 10px;
  padding: 0px;
  margin: 0px;
  font-size: 1px;
  background-color:black;
}

.calc-btn-small-alt-left {
  display: inline-block;
  width: 18.5px;
  margin: 0px 0px 0px 4px;
  padding: 0px;
  text-align: left;
  color: rgb(158, 152, 55);
  font-weight: bold;
  background-color: red;
}

.calc-btn-small-alt-right {
  display: inline-block;
  width: 18px;
  margin: 0px 4px 0px 0px;
  padding: 0px;
  text-align: right;
  color: rgb(175, 90, 119);
  font-weight: bold;
  background-color: blue;
}

.calc-btn-small-alt-center {
  display: inline-block;
  width: 36.5px;
  margin: 0px 1px 0px 1px;
  padding: 0px;
  text-align: center;
  color: rgb(158, 152, 55);
  font-weight: bold;
  background-color:black;
}

.cal-btn-grey {
  background-color: rgb(110, 118, 121);
}

.cal-btn-purple {
  background-color: rgb(99, 98, 173);
}

.cal-btn-orange {
  background-color: rgb(182, 173, 103);
}

.cal-btn-red {
  background-color: rgb(175, 84, 115);
}

#myModalLabel
{
	font-family: Impact, Charcoal, sans-serif;
	font-size: 18px;
}
              
            
!

JS

              
                $( window ).resize(function() {
  $( "#calculator" ).attr("zoom") ;
});


// Global variables to store calculator settings
var calculator =
    {
      previousAnswer: 0,
      justCalculated: false,
      degreeOrRadians: "degree",
    }
// This function append the supplied argument to the calculator display screen
function appendCalcScreen(inputString)
{
  $("textarea.calc-screen").val($("textarea.calc-screen").val() + inputString);
}

function backspaceCalcScreen()
{
  var currentCalcScreenValue = $("textarea.calc-screen").val();
  if (currentCalcScreenValue.length > 0)
    {
      $("textarea.calc-screen").val(currentCalcScreenValue.substring(0, currentCalcScreenValue.length - 1));
    }
}

function clearScreen()
{
  $("textarea.calc-screen").val("");
}

// Defines the tokens and their properties.
var nonNumericTokensDefinitions = 
[
  {lexeme: "+", category:"operator", associativity:"left", precedence:1, evalFunction: (function(LHS, RHS) {return LHS+RHS;})},
  {lexeme: "-", category:"operator", associativity:"left", precedence:1, evalFunction: (function(LHS, RHS) {return LHS-RHS;})},
  {lexeme: "*", category:"operator", associativity:"left", precedence:2, evalFunction: (function(LHS, RHS) {return LHS*RHS;})},
  {lexeme: "/", category:"operator", associativity:"left", precedence:2, evalFunction: (function(LHS, RHS) {return LHS/RHS;})},
  {lexeme: "^", category:"operator", associativity:"right", precedence:3, evalFunction: (function(LHS, RHS) {return Math.pow(LHS,RHS);})},
  {lexeme: "-u", category:"function", evalFunction: (function(RHS) {return -1.0*RHS;})},
  {lexeme: "=", category:"operator", associativity:"right", precedence:0},
  {lexeme: "log", category:"function", evalFunction: (function(RHS) {return Math.log10(RHS);})},
  {lexeme: "ln", category:"function", evalFunction: (function(RHS) {return Math.log(RHS);})},
  {lexeme: "sin", category:"function", evalFunction: (function(RHS) {return Math.sin(RHS);})},
  {lexeme: "asin", category:"function", evalFunction: (function(RHS) {return Math.asin(RHS);})},
  {lexeme: "cos", category:"function", evalFunction: (function(RHS) {return Math.cos(RHS);})},
  {lexeme: "acos", category:"function", evalFunction: (function(RHS) {return Math.acos(RHS);})},
  {lexeme: "tan", category:"function", evalFunction: (function(RHS) {return Math.tan(RHS);})},
  {lexeme: "atan", category:"function", evalFunction: (function(RHS) {return Math.atan(RHS);})},
  {lexeme: "Ans", category:"variable", evalFunction: (function() {return calculator.previousAnswer;})},
  {lexeme: "(", category:"bracket"},
  {lexeme: ")", category:"bracket"}
];

function evaulatePostfixTokens(tokenPostfixArray)
{
  var i = 0;
  while ((i < tokenPostfixArray.length) && (tokenPostfixArray.length !== 1))
    {
      var currentPostfixToken = tokenPostfixArray[i];
      var currentPostfixTokenCategory = getTokenCategory(currentPostfixToken);
      
      if ($.isNumeric(currentPostfixToken))
      {
        i++;
        continue;
      }
      else if (currentPostfixTokenCategory === "function")
        {
          // If the function is at the start of the Postfix Token and has no parameter, flag n error
          if (i < 1)
            {
              return null;
            }
          else if (($.isNumeric(tokenPostfixArray[i-1])) === true)
            {
              previousPostfixToken = tokenPostfixArray[i-1];
              var functionEvaulationResult = getTokenEvalFunction(currentPostfixToken)(previousPostfixToken);
              tokenPostfixArray.splice(i-1,2,functionEvaulationResult);
              i = i - 1;
              
              // Deal with the case when user specify something like 5log4, where there is an implicit *
              if (($.isNumeric(tokenPostfixArray[i-1])) === true)
              {
                tokenPostfixArray.splice(i-1,2,tokenPostfixArray[i-1]*functionEvaulationResult);
                i = i - 1;                
              }              
            }
          else
            {
              return null;
            }                                               
        }
      else if (currentPostfixTokenCategory === "operator")
        {
          // Check if there is sufficient number of operands 
          if (i < 2)
            {
              // Insufficient number of operands, return error
              return null;
            }
          // Check if the two items in front of the operator are numbers
          else if ((($.isNumeric(tokenPostfixArray[i-1])) === true) && (($.isNumeric(tokenPostfixArray[i-2])) === true))
            {
              // Evaulate the operator 
              var functionEvaulationResult = getTokenEvalFunction(currentPostfixToken)(tokenPostfixArray[i-2],tokenPostfixArray[i-1]);
              
              // Replace the operator and operands with the result
               tokenPostfixArray.splice(i-2,3,functionEvaulationResult);
              
              // Shift our scanner location
               i = i - 2;
                            
            }
          else 
            {
              return null
            }
        }
    }

   // Deal with input where user specify 5(4*2) where there is an implicit * before brackets
   if (($.isNumeric(tokenPostfixArray[i-1])) === true)
   {
      tokenPostfixArray.splice(i-2,2,tokenPostfixArray[i-1]*tokenPostfixArray[i-2]);
      i = i - 2;                
   } 
  return tokenPostfixArray[0];
}

function getTokenProperty(inputLexeme, property)
{
  for (var i = 0; i < nonNumericTokensDefinitions.length; i++)
    {
      if (nonNumericTokensDefinitions[i].lexeme === inputLexeme)
        {
          return nonNumericTokensDefinitions[i][property];
        }
    }
  return null;
}

function getTokenEvalFunction(inputLexeme)
{
  return getTokenProperty(inputLexeme, "evalFunction");
}
function getTokenPrecedence(inputLexeme)
{
  return getTokenProperty(inputLexeme, "precedence");
}

function getTokenAssociativity(inputLexeme)
{
  return getTokenProperty(inputLexeme, "associativity");
}
  
function getTokenCategory(inputLexeme)
{
  return getTokenProperty(inputLexeme, "category");
}
function identifyNonNumericToken(inputStringArgument)
{
  var matchedTokenLexeme = null;  
  // Loop through the tokens definition to find a match
  for (var i = 0; i < nonNumericTokensDefinitions.length; i++)
    {
      currentTokenDefinition = nonNumericTokensDefinitions[i];
      // See if our token matches our provided string
      if (currentTokenDefinition.lexeme === inputStringArgument.substring(0,currentTokenDefinition.lexeme.length))
          {
            matchedTokenLexeme = currentTokenDefinition.lexeme;
            return matchedTokenLexeme;
          }
    }
  return matchedTokenLexeme;
}

// This function goes through a token array and identify any unery operators and provide a "u" postfix for identification
function processUneryOperators(inputTokenArray)
{
    for (var i = 0; i < inputTokenArray.length; i++)
      {
        
        if (inputTokenArray[i] === "Ans")
          {
            inputTokenArray[i] = calculator.previousAnswer;
          }
        // Identify and flag unery "-" operator
        if (inputTokenArray[i] === "-")
        {
          var previousToken = inputTokenArray[i-1];
          var nextToken = inputTokenArray[i+1];
 
          if (
            (i === 0) || 
            (getTokenCategory(previousToken) === "operator") ||
            (previousToken == "(") ||
            (getTokenCategory(nextToken) === "function")
            )
          {
            inputTokenArray[i] = "-u";
          }
        }
      }
  return inputTokenArray;
}

function tokenize(inputStringArgument)
{
  // Array of tokens that are to be returned
  var tokenArray = [];
  
  // Temporary placeholder for the current token as we parse the string
  var currentToken ="";
  
  // Remove unwanted whitespace
  var inputString = inputStringArgument.replace(" ","");
  
  console.log("Input String: " + inputString);
  
  // Start parsing our string from left to right
  for (var i = 0; i < inputString.length; i++)
    {
      // Test for numeric and decimals
      if (($.isNumeric(inputString[i])) || (inputString[i] === "."))
        {
          // If the current token (so far) is numeric, we append this char to it
          if ($.isNumeric(currentToken) || (currentToken === ""))
            {
              currentToken += inputString[i];
            }
        }
      // Test the non-numeric value to match operators and functions
      else
        {
          // We have found a non-numeric value, we will push any numeric token to the tokenArray
          if ($.isNumeric(currentToken))
            {
              // Push into the tokenArray as a number (converted from token string)
              tokenArray.push(Number(currentToken));
              currentToken = "";                              
            }
          
          // We now match this non-numeric value to a token lexeme
          currentToken = identifyNonNumericToken(inputString.substring(i));
          
          // If we have found a valid non-numeric token
          if (currentToken !== null)
            {
              tokenArray.push(currentToken);
              // Advance our scanner forward by the lexueme's length less 1 (due to the i++ in the loop)
              i += currentToken.length - 1;
              currentToken = "";
            }
          else
            {
              // We have not found a valid token, return error.
              return null;
            }
        }
      
    // If we are at the end of our input string, push the last token to the array if it's not empty (numeric literal)
    if ((i === (inputString.length - 1)) && (currentToken !== ""))
      {
        $.isNumeric(currentToken) ? tokenArray.push(Number(currentToken)) : tokenArray.push(currentToken);
      }
      
    }
  
  return tokenArray;
}

function convertInfixTokenArraytoPostFix(infixTokenArray)
{
  var postfixResult =[];
  var operatorStack=[];
  
  for (var i =0; i < infixTokenArray.length; i++)
    {
      currentToken = infixTokenArray[i];
      if ($.isNumeric(currentToken))
        {
          postfixResult.push(currentToken);
          
          // Check if the top token of the opstack is a function, if so, pop it into the postfix result
          while (operatorStack.length >0)
            {
              operatorStackTopToken = operatorStack[operatorStack.length - 1];
              if (getTokenCategory(operatorStackTopToken) === "function")
              {
                postfixResult.push(operatorStack.pop());
              }
              else
                {
                  break;
                }
            }
        }
      else if (getTokenCategory(currentToken) === "variable")
         {
           operatorStack.push(currentToken);
         }
      else if (getTokenCategory(currentToken) === "function")
        {
          operatorStack.push(currentToken);
        }
      else if (getTokenCategory(currentToken) == "operator")
        {
          while (operatorStack.length > 0)
            {
              operatorStackTopToken = operatorStack[operatorStack.length - 1];
              if (getTokenCategory(operatorStackTopToken) === "operator")
                {
                  var opStackTopTokenAssociativity = getTokenAssociativity(operatorStackTopToken);
                  var opStackTopTokenPrecedence = getTokenPrecedence(operatorStackTopToken);
                  var currentTokenAssociativity = getTokenAssociativity(currentToken);
                  var currentTokenPrecedence = getTokenPrecedence(currentToken);
                  
                  if (
                    ((currentTokenAssociativity === "left") && (currentTokenPrecedence <= opStackTopTokenPrecedence))
                    ||
                    ((currentTokenAssociativity === "right") && (currentTokenPrecedence < opStackTopTokenPrecedence)))
                    {
                      postfixResult.push(operatorStack.pop());
                    }
                  else
                    {
                      break;
                    }
                }
              else
                {
                  break;
                }
            }
          operatorStack.push(currentToken);
        }
      else if(currentToken === "(")
        {
          operatorStack.push(currentToken);
        }
      else if(currentToken === ")")
        {
          do 
          {
            operatorStackTopToken = operatorStack[operatorStack.length - 1];
            if (operatorStackTopToken !== "(")
              {
                postfixResult.push(operatorStack.pop());
              }
              else
              {
                operatorStack.pop();
                // Check if it's a pair of bracket enclosed for a function ie. cos(1+2), if so, pop the opstack into the postfix result
                while (operatorStack.length >0)
                  {
                    operatorStackTopToken = operatorStack[operatorStack.length - 1];
                    if (getTokenCategory(operatorStackTopToken) === "function")
                      {
                      postfixResult.push(operatorStack.pop());
                      }
                    else
                      {
                        break;
                      }
                  }
                break;
              }
            } while (operatorStack.length > 0)
        }
    }
  
  while (operatorStack.length > 0)
    {
      postfixResult.push(operatorStack.pop());
    }
      
   return postfixResult;
}

function executeCalculate()
{
  var processedTokenArray = tokenize($("textarea.calc-screen").val());
  console.log(processedTokenArray);
  processedTokenArray = processUneryOperators(processedTokenArray);
  console.log(processedTokenArray);
  processedTokenArray = convertInfixTokenArraytoPostFix(processedTokenArray);
  console.log(processedTokenArray);
  result = evaulatePostfixTokens(processedTokenArray);
  console.log(result);
  
  calculator.justCalculated = true;
  
  // Write the result to screen, or shows "Error" if any error occured.
  if (result !== null)
    {
      $("textarea.calc-screen").val(result);
      calculator.previousAnswer = result;
    }
  else
    {
      $("textarea.calc-screen").val("Error");
    }
}

$(document).ready(
  function()
  {
    
  }
);
//////////////////////////////
// Capture keyboard events. //
//////////////////////////////

// Keydown function to capture "special" keys
$(document).keydown(function(){
  // Key that applies even when user has the calculator screen TextArea focused.
  //console.log(event.which);
  switch (event.which)
    {
      case 13:
        executeCalculate();
        event.preventDefault();
        break;
     case 27:
        $("[ccmd=AC]").trigger("click");
        break;        
    }
  
  // If user doesn't have the calculator screen TextArea focused, we want to capture the keyboard events still
  if (($(document.activeElement)).attr("id") !== "calc-screen")
  {
    //console.log(event.which);

     // Intercept certain keystrokes to link to special functions:
    switch (event.which)
      {
       // User pressed "Enter", trigger the execute button
        case 13:
          executeCalculate();
          event.preventDefault();
          //backspaceCalcScreen();
          break;
          // User pressed "Shift"
        case 16:
          break;
          // User pressed "Escape", press the AC button to clear screen
        case 27:
          $("[ccmd=AC]").trigger("click");
          break;
          // User pressed "Backspace", press the DEL button
        case 8:
          event.preventDefault();
          $("[ccmd=DEL]").trigger("click");
          break;          
      }
  }
});

// Keypress function for all other "standard" keys
$(document).keypress(function(){
  // If user doesn't have the calculator screen TextArea focused, we want to capture the keyboard events still
  if (($(document.activeElement)).attr("id") !== "calc-screen")
  {
        if (calculator.justCalculated === true)
        {
          calculator.justCalculated = false;
          clearScreen();
        }
    
        appendCalcScreen(String.fromCharCode(event.which));
  }
});

function appendAnsIfRequired()
  {
    if (calculator.justCalculated === true)
        {
          calculator.justCalculated = false;
          clearScreen();
          appendCalcScreen("Ans");
        }
    return;
  }

  function clearScreenIfRequired()
  {
    if (calculator.justCalculated === true)
        {
          calculator.justCalculated = false;
          clearScreen();
        }
    return;    
  }
  
// Event to convert clicks on buttons to their correct functions
$(".calc-btn, .calc-btn-small").click(function(){
  var ButtonCommand = $(this).attr("ccmd");
  
  switch (ButtonCommand)
  {
    // User pressed all clear to clear screen
    case "AC":
      clearScreen();
      break;
    // Call the parser to evaulate what's on screen
    case "EXECUTE":
      executeCalculate();
      break;
    case "DEL":
      backspaceCalcScreen();
      break;
    case "ADD":
      appendAnsIfRequired();
      appendCalcScreen("+");
      break;
    case "MINUS":
      appendAnsIfRequired();
      appendCalcScreen("-");
      break;
    case "MULTIPLY":
      appendAnsIfRequired();
      appendCalcScreen("*");
      break;
    case "DIVIDE":
      appendAnsIfRequired();
      appendCalcScreen("/");
      break;
    case "SQUARED":
      appendAnsIfRequired();
      appendCalcScreen("^2");
      break;
    case "POWER":
      appendAnsIfRequired();
      appendCalcScreen("^");
      break;
    case "DECIMAL POINT":
      appendCalcScreen(".");
      break;
    // Exponent in scientific notation
    case "EXPONENT":
      appendAnsIfRequired();
      appendCalcScreen("*10^");
      break;
    case "UNERY NEGATIVE":
      clearScreenIfRequired();
      appendCalcScreen("(-1)*");
      break;
    case "FIT":
     // window.open(this.href,"_self","width=290, height=520, location=no, menubar=no, status=no, toolbar=no");
      window.open(this.href, "Calculator", "width=320, height=520");
      break;
    case undefined:
      clearScreenIfRequired();
      appendCalcScreen($(this).html());
  }

});
              
            
!
999px

Console