<script>
<!--
 var state=0;
 var result = 0;
 function clr(f)
  { f.display.value  = '';   state=0;}
 function number(f,n)
  {
   if (state==3)
    {
     clr(f);
    }
   f.display.value  += n;
   state=1;
  }
 function point(f)
  { number(f, '.'); }
 function bs(f)
  {
   var s = f.display.value;
   if (state == 3)
    {return;}
   if (eval(s.length) > 0)
    {
      s.length -= 1;
      f.display.value = s;
      if (state == 2)
	   { state = 1;}
      if (s.length == 0)
	   { state = 0;}
    }
  }
 function op(f,o)
  {
   if (state==3)
    {
     f.display.value  = result;
     f.display.value  += o;
     state = 2;
    }
   if (state==1)
    {
     f.display.value  += o;
     state = 2;
    }
  }
 function add(f)
  { op(f,'+') }
 function subtract(f)
  { op(f,'-') }
 function multiply(f)
  { op(f,'*') }
 function divide(f)
  {
   if (f==0)
    {
     f.display.value  = "error";
     state = 0;
	}
   else
    { op(f,'/')}
  }
 function equals(f)
  {
   if (state == 3)
    { return; }
   result = eval(f.display.value);
   f.display.value += ' = ' + result;
   state=3;
  }
//-->
</script>

<form>
<center>
 <table border="0" cellPadding="3" cellSpacing="0">
  <tbody>
   <tr>
    <td align="middle" colSpan="5"><INPUT name=display><br></td></tr>
     <tr>
      <td align=middle><input onclick=number(this.form,7) style="width: 20px" type=button value=" 7 "></td>
      <td align=middle><input onclick=number(this.form,8) style="width: 20px" type=button value=" 8 "></td>
      <td align=middle><input onclick=number(this.form,9) style="width: 20px" type=button value=" 9 "></td>
      <td align=middle><input onclick=add(this.form) style="width: 20px" type=button value=" + "></td>
      <td align=middle><input onclick=clr(this.form) style="width: 30px" type=button value=" cl "></td>
    </tr>
    <tr>
     <td align=middle><input onclick=number(this.form,4) style="width: 20px" type=button value=" 4 "></td>
     <td align=middle><input onclick=number(this.form,5) style="width: 20px" type=button value=" 5 "></td>
     <td align=middle><input onclick=number(this.form,6) style="width: 20px" type=button value=" 6 "></td>
     <td align=middle><input onclick=subtract(this.form) style="width: 20px" type=button value=" - "></td>
     <td align=middle></td>
	</tr>
    <tr>
     <td align=middle><input onclick=number(this.form,1) style="width: 20px" type=button value=" 1 "></td>
     <td align=middle><input onclick=number(this.form,2) style="width: 20px" type=button value=" 2 "></td>
     <td align=middle><input onclick=number(this.form,3) style="width: 20px" type=button value=" 3 "></td>
     <td align=middle><input onclick=multiply(this.form) style="width: 20px" type=button value=" * "></td>
     <td align=middle> </td>
	</tr>
    <tr>
     <td align=middle colspan=2><input onclick=number(this.form,0) style="width: 48px" type=button value="   0   "></td>
     <td align=middle><input onclick=point(this.form) style="width: 20px" type=button value=" . "></td>
     <td align=middle><input onclick=divide(this.form) style="width: 20px" type=button value=" / "></td>
     <td align=middle><input onclick=equals(this.form) style="width: 30px" type=button value="  =  "></td>
   </tr>
  </tbody>
 </table>
</center>