Sorry for the delay - it is now completed.
<html>
<head>
<title>Step 3</title>
<link rel="stylesheet" href="calc.css">
<script language="javascript">
var stat=-1; //no calculation pending
var result=0; //no result yet
function dosign() {
cleanup(); //checks for pending calculation
if(console.value=="0") {return;}
if(console.value.indexOf('-')==-1) {console.value='-'+console.value;return;}
console.value=console.value.substring(1,console.value.length);
}
function cdot() {
cleanup(true); //checks for pending calculation
if(console.value.indexOf('.')!=-1) {return;}
console.value+=".";
}
function cdigit(element) {
cleanup(true); //checks for pending calculation
if(console.value=="0") {console.value="";}
console.value+=element.value;
}
function bkspc() {
if(console.value.length<2) {console.value="0"; return;}
console.value=console.value.substring(0,console.value.length-1);
}
function cls() {
console.value="0";
}
function clearScreen() {
cls();
result=0;
stat=-1;
}
function cleanup(clear) {
var con=parseInt(console.value);
if(stat==1) {stat=2}
else if(stat==2) {
//evaluation is done when status is 2
switch(lsign) {
case "+":
result+=con;
break;
case "-":
result-=con;
break;
case "*":
result*=con;
break;
case "/":
result/=con;
break;
default:
alert(lsign);
break;
}
stat=0; //reset
}
//conditionally clean screen
if(clear) cls();
return;
}
var lsign=""; //stores the last sign pressed
function esign(txt) {
//operators that warrant immediate calculation
var con=parseInt(console.value);
switch(txt.value) {
case "sqrt":
console.value=Math.sqrt(con);
break;
case "1/X":
var res=(1/con).toString();
if(res.length>20) {res=res.substring(0,19)}
console.value=res;
break;
}
//Note that no actual evaluation is done here
var con=parseInt(console.value);
if(stat==-1) {result=con;} //saves current screen buffer as result
stat=1; //a sign has been pressed, waiting for user to enter digits
lsign=txt.value; //this stores the current sign pressed
result=con;
}
function calc() {
cleanup();
console.value=result;
}
</script>
</head>
<body>
<table class="calc">
<tr><td colspan="5"><input type="text" readonly="true" id="console" class="console" value="0"></td></tr>
<tr class="cline2">
<td colspan="5">
<input type="button" onclick="bkspc();" value=" Backspace ">
<input type="button" onclick="clearScreen();" value=" CE ">
<input type="button" onclick="clearScreen();" value=" C ">
</td></tr>
<tr class="cline">
<td><input type="button" value="7" onclick="cdigit(this);"></td>
<td><input type="button" value="8" onclick="cdigit(this);"></td>
<td><input type="button" value="9" onclick="cdigit(this);"></td>
<td><input type="button" value="/" onclick="esign(this)"></td>
<td><input type="button" value="sqrt" onclick="esign(this)"></td>
</tr>
<tr class="cline">
<td><input type="button" value="4" onclick="cdigit(this);"></td>
<td><input type="button" value="5" onclick="cdigit(this);"></td>
<td><input type="button" value="6" onclick="cdigit(this);"></td>
<td><input type="button" value="*" onclick="esign(this)"></td>
<td><input type="button" value="%" onclick="esign(this)"></td>
</tr>
<tr class="cline">
<td><input type="button" value="1" onclick="cdigit(this);"></td>
<td><input type="button" value="2" onclick="cdigit(this);"></td>
<td><input type="button" value="3" onclick="cdigit(this);"></td>
<td><input type="button" value="-" onclick="esign(this)"></td>
<td><input type="button" value="1/X" onclick="esign(this)"></td>
</tr>
<tr class="cline">
<td><input type="button" value="0" onclick="cdigit(this);" ></td>
<td><input type="button" value="+/-" onclick="dosign();" ></td>
<td><input type="button" value="." onclick="cdot();" ></td>
<td><input type="button" value="+" onclick="esign(this)"></td>
<td><input type="button" value="=" onclick="calc()"></td>
</tr>
</table>
</body>
</html>
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