JavaScript Calculator

Instructions:

1: Copy and paste the following style declaration in the HEAD section of your page:
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2: Copy and paste the following javascript in the HEAD section of your page:
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var whichkey;

function setnum(num){
if((document.f.answer.value!='')&&num1set)document.f.answer.value='';
if(num1set){
num2+=num;
document.f.answer.value=num2;
}else{
num1+=num;
document.f.answer.value=num1;
}}

function setoper(oper){
if(num1set&&(document.f.answer.value!='')&&(num2==''))operation=oper;
if(num1set&&(operation!='')&&(num2!=''))docalc(oper);
if(!num1set){
operation=oper;
num1=document.f.answer.value;
num1set=true;
}}

function backsp(){
if(document.f.answer.value.length>=1){
document.f.answer.value=document.f.answer.value.substring(0,document.f.answer.value.length-1);
if(num1set) num2=document.f.answer.value;
else num1=document.f.answer.value;
}}

function testdot(){
if(num1set) if(num2.indexOf('.')==(-1))setnum('.');
else if(num1.indexOf('.')==(-1))setnum('.');
}

function clearall(yes){
if(yes){
num1='';
num2='';
num1set=false;
operation='';
}else num2='';
document.f.answer.value=num1;
}

function negate(){
if(num1set){
if(num2!=''){
num2=-num2;
document.f.answer.value=num2;
}}else{
if(num1!=''){
num1=-num1;
document.f.answer.value=num1;
}}}

function percent(){
if((num1!='')&&(num2!='')){
num2=''+((parseFloat(num2))/100*parseFloat(num1));
document.f.answer.value=num2;
}}

function invert(){
if(num1set){
if(num2!=''){
num2=''+1/parseFloat(num2);
document.f.answer.value=num2;
}}else{
if(num1!=''){
num1=''+1/parseFloat(num1);
document.f.answer.value=num1;
}}}

function checkbx(){
(inmem!='')? document.f.box.checked=true: document.f.box.checked=false;
alert('Do not click here.\n\nThis is to show if you have something in memory.');
document.f.box.blur();
}

if(ns4){
window.captureEvents(Event.KEYPRESS);
window.onkeypress=showkeypress;
}else document.onkeypress=showkeypress;
</script>

3: Copy and paste the following HTML in the BODY section of your page:
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<form name="f">
<table cellspacing="0" cellpadding="6" border="0" bgcolor="#006bae">
<tr><td colspan="6" bgcolor="lightgrey" align="center"><b>JavaScript Calculator</b></td></tr>
<tr>
<td align="center" colspan="6">
<input type="text" class="answer" size="30" name="answer">
</td>
</tr>
<tr>
<td align="center" colspan="6">
<input type="checkbox" onClick="checkbx()" name="box"> Mem    
<input type="button" value="Backspace" onClick="this.blur(); backsp()">    
<input type="button" value="    CE    " onClick="this.blur(); clearall(false)">    
<input type="button" value="     C     " onClick="this.blur(); clearall(true)">
</td>
</tr>
<tr>
<td align="center"><input type="button" class="bttnop" value="  MC  " onClick="this.blur(); memory(0)"></td>
<td align="center"><input type="button" class="bttn" value="   7   " onClick="this.blur(); setnum('7')"></td>
<td align="center"><input type="button" class="bttn" value="   8   " onClick="this.blur(); setnum('8')"></td>
<td align="center"><input type="button" class="bttn" value="   9   " onClick="this.blur(); setnum('9')"></td>
<td align="center"><input type="button" class="bttnop" value="   /    " onClick="this.blur(); setoper('/')"></td>
<td align="center"><input type="button" class="bttnop" value=" sqrt " onClick="this.blur(); squareroot()"></td>
</tr>
<tr>
<td align="center"><input type="button" class="bttnop" value="  MR  " onClick="this.blur(); memory(1)"></td>
<td align="center"><input type="button" class="bttn" value="   4   " onClick="this.blur(); setnum('4')"></td>
<td align="center"><input type="button" class="bttn" value="   5   " onClick="this.blur(); setnum('5')"></td>
<td align="center"><input type="button" class="bttn" value="   6   " onClick="this.blur(); setnum('6')"></td>
<td align="center"><input type="button" class="bttnop" value="   *    " onClick="this.blur(); setoper('*')"></td>
<td align="center"><input type="button" class="bttnop" value="  %  " onClick="this.blur(); percent()"></td>
</tr>
<tr>
<td align="center"><input type="button" class="bttnop" value="  MS  " onClick="this.blur(); memory(2)"></td>
<td align="center"><input type="button" class="bttn" value="   1   " onClick="this.blur(); setnum('1')"></td>
<td align="center"><input type="button" class="bttn" value="   2   " onClick="this.blur(); setnum('2')"></td>
<td align="center"><input type="button" class="bttn" value="   3   " onClick="this.blur(); setnum('3')"></td>
<td align="center"><input type="button" class="bttnop" value="   -    " onClick="this.blur(); setoper('-')"></td>
<td align="center"><input type="button" class="bttnop" value="  1/x " onClick="this.blur(); invert()"></td>
</tr>
<tr>
<td align="center"><input type="button" class="bttnop" value="  M+  " onClick="this.blur(); memory(3)"></td>
<td align="center"><input type="button" class="bttn" value="   0   " onClick="this.blur(); setnum('0')"></td>
<td align="center"><input type="button" class="bttnop" value="  +/-  " onClick="this.blur(); negate()"></td>
<td align="center"><input type="button" class="bttn" value="   .    " onClick="this.blur(); testdot()"></td>
<td align="center"><input type="button" class="bttnop" value="   +   " onClick="this.blur(); setoper('+')"></td>
<td align="center"><input type="button" class="bttnop" value="  =   " onClick="this.blur(); docalc('')"></td>
</tr>
</table>
</form>

JavaScript Calculator

Mem