<script>
function inserisci(numero) {
var valore = document.getElementById('display').value;
document.getElementById('display').value = valore + numero;
}
function cancella() {
var len = document.getElementById('display').value.length;
var str = document.getElementById('display').value.substr(0,len-1);
document.getElementById('display').value=str;
}
</script>
<form action="login.php" method="post">
<table>
<tr>
<td colspan="3">
<input type="text" size="13" id="display" name="display" onload="focus()"/>
</td>
</tr>
<tr>
<td>
<input type="button" id="1" value="1" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="button" id="2" value="2" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="button" id="3" value="3" onclick="inserisci(this.value)"/>
</td>
</tr>
<tr>
<td>
<input type="button" id="4" value="4" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="button" id="5" value="5" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="button" id="6" value="6" onclick="inserisci(this.value)"/>
</td>
</tr>
<tr>
<td>
<input type="button" id="7" value="7" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="button" id="8" value="8" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="button" id="9" value="9" onclick="inserisci(this.value)"/>
</td>
</tr>
<tr>
<td>
<input type="button" id="C" value="C" onclick="cancella()"/>
</td>
<td>
<input type="button" id="0" value="0" onclick="inserisci(this.value)"/>
</td>
<td>
<input type="submit" id="login" value="Login"/>
</td>
</tr>
</table>
</form>