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<html>
<head>
<title>Web Based Calculator</title>
</head>
<body>
<script language="javascript">
<!-- hide this script tag's contents from old browsers
function addChar(input, character)
{
if(input.value == null || input.value == "0")
input.value = character
else
input.value += character
}
function deleteChar(input)
{
input.value = input.value.substring(0, input.value.length - 1)
}
function changeSign(input)
{
// could use input.value = 0 - input.value, but let's show off substring
if(input.value.substring(0, 1) == "-")
input.value = input.value.substring(1, input.value.length)
else
input.value = "-" + input.value
}
function compute(form)
{
form.display.value = eval(form.display.value)
}
function square(form)
{
form.display.value = eval(form.display.value) * eval(form.display.value)
}
function checkNum(str)
{
for (var i = 0; i < str.length; i++) {
var ch = str.substring(i, i+1)
if (ch < "0" || ch > "9") {
if (ch != "/" && ch != "*" && ch != "+" && ch != "-"
&& ch != "(" && ch!= ")") {
alert("invalid entry!")
return false
}
}
}
return true
}
<!-- done hiding from old browsers -->
</script>
<form>
<div align="center"><center><table border="5" align="center"
bordercolordark="#800000" bgcolor="#C0C0C0">
<tr align="center">
<td colspan="4"><table border="3" width="250">
<tr>
<td align="center" width="236"><input name="display" value="0" size="32"></td>
</tr>
</table>
</td>
</tr>
<tr align="center">
<td><input type="button" value=" 7 " onClick="addChar(this.form.display, '7')"> </td>
<td><input type="button" value=" 8 " onClick="addChar(this.form.display, '8')"> </td>
<td><input type="button" value=" 9 " onClick="addChar(this.form.display, '9')"> </td>
<td><input type="button" value=" / " onClick="addChar(this.form.display, '/')"> </td>
</tr>
<tr align="center">
<td><input type="button" value=" 4 " onClick="addChar(this.form.display, '4')"> </td>
<td><input type="button" value=" 5 " onClick="addChar(this.form.display, '5')"> </td>
<td><input type="button" value=" 6 " onClick="addChar(this.form.display, '6')"> </td>
<td><input type="button" value=" * " onClick="addChar(this.form.display, '*')"> </td>
</tr>
<tr align="center">
<td><input type="button" value=" 1 " onClick="addChar(this.form.display, '1')"> </td>
<td><input type="button" value=" 2 " onClick="addChar(this.form.display, '2')"> </td>
<td><input type="button" value=" 3 " onClick="addChar(this.form.display, '3')"> </td>
<td><input type="button" value=" - " onClick="addChar(this.form.display, '-')"> </td>
</tr>
<tr align="center">
<td><input type="button" value=" 0 " onClick="addChar(this.form.display, '0')"> </td>
<td><input type="button" value=" . " onClick="addChar(this.form.display, '.')"> </td>
<td><input type="button" value=" +/- " onClick="changeSign(this.form.display)"> </td>
<td><input type="button" value=" + " onClick="addChar(this.form.display, '+')"> </td>
</tr>
<tr align="center">
<td><input type="button" value=" ( " onClick="addChar(this.form.display, '(')"> </td>
<td><input type="button" value=" ) " onClick="addChar(this.form.display, ')')"> </td>
<td><input type="button" value=" sq "
onClick="if (checkNum(this.form.display.value))
{ square(this.form) }"> </td>
<td><input type="button" value=" <- " onClick="deleteChar(this.form.display)"> </td>
</tr>
<tr align="center">
<td colspan="2"><input type="button" value=" Enter " name="enter"
onClick="if (checkNum(this.form.display.value))
{ compute(this.form) }"> </td>
<td colspan="2"><input type="button" value=" C "
onClick="this.form.display.value = 0 "> </td>
</tr>
</table>
</center></div>
</form>
</body>
</html>
