普通的计算器，只有加减乘除运算，支持小数点

<script language="JavaScript">

</script>
<form name="calc">
<table border=1>
<td colspan=4><input type="text" name="expr" size=30 action="compute(this.form)"> <tr>
<td><input type="button" value=" 7 " onClick="enter(this.form, seven)">
<td><input type="button" value=" 8 " onClick="enter(this.form, eight)">
<td><input type="button" value=" 9 " onClick="enter(this.form, nine)">
<td><input type="button" value="   / " onClick="enter(this.form, divide)">
<tr><td><input type="button" value=" 4 " onClick="enter(this.form, four)">
<td><input type="button" value=" 5 " onClick="enter(this.form, five)">
<td><input type="button" value=" 6 " onClick="enter(this.form, six)">
<td><input type="button" value=" * " onClick="enter(this.form, multiply)">
<tr><td><input type="button" value=" 1 " onClick="enter(this.form, one)">
<td><input type="button" value=" 2 " onClick="enter(this.form, two)">
<td><input type="button" value=" 3 " onClick="enter(this.form, three)">
<td><input type="button" value="   - " onClick="enter(this.form, minus)">
<tr><td colspan=2><input type="button" value="       0       " onClick="enter(this.form, zero)">
<td><input type="button" value="   . " onClick="enter(this.form, decimal)">
<td><input type="button" value=" + " onClick="enter(this.form, plus)">
<tr><td colspan=2><input type="button" value="   =   " onClick="compute(this.form)">
<td colspan=2><input type="button" value="AC" size= 3 onClick="clear(this.form)"> </table>
</form>