Untitled

<html>
  <head>
    <title>Calolatrice</title>
    <script type=text/javascript>
      var SchiacciatoOperatore = true, OperazionePrecedente = "=", Accumulatore = 0;
      function Cifra(Out, Valore) {
        if (SchiacciatoOperatore || Out.value == "0")  { Out.value = ""; SchiacciatoOperatore = false; }
        Out.value += Valore
      }
      function Operatore(Out, Valore) {

        switch(OperazionePrecedente) {
          case "/":  if (Out.value == "0")  alert("divisione per zero!!!");
                     else Out.value = Accumulatore / Number(Out.value);
                     break;
          case "*":  Out.value = Accumulatore * Number(Out.value);
                     break;
          case "-":  Out.value = Accumulatore - Number(Out.value);
                     break;
          case "+":  Out.value = Accumulatore + Number(Out.value);
                     break;
          case "=":  // l'uguale conclude, dunque non fa azioni proprie
                     break;
        }
        SchiacciatoOperatore = true; OperazionePrecedente = Valore;  Accumulatore = Number(Out.value);
      }
      function CambiaSegno(Out) {
        Out.value = -Number(Out.value)
      }
     </script>
  </head>
  <body>
    <form name=Calc>
      <table align=center>
        <tr>
          <td colspan=4><input type=text name=Display value="0" style="width:100%;text-align:right"></td>
        </tr><tr>
          <td><input type=button value="7" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="8" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="9" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="/" style="width:20pt;height:20pt" onclick='javascript: Operatore(Calc.Display, this.value)'></td>
        </tr><tr>
          <td><input type=button value="4" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="5" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="6" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="*" style="width:20pt;height:20pt" onclick='javascript: Operatore(Calc.Display, this.value)'></td>
        </tr><tr>
          <td><input type=button value="1" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="2" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="3" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="-" style="width:20pt;height:20pt" onclick='javascript: Operatore(Calc.Display, this.value)'></td>
        </tr><tr>
          <td><input type=button value="0" style="width:20pt;height:20pt" onclick='javascript: Cifra(Calc.Display, this.value)'></td>
          <td><input type=button value="+/-" style="width:20pt;height:20pt" onclick='javascript: CambiaSegno(Calc.Display)'></td>
          <td><input type=button value="=" style="width:20pt;height:20pt" onclick='javascript: Operatore(Calc.Display, this.value)'></td>
          <td><input type=button value="+" style="width:20pt;height:20pt" onclick='javascript: Operatore(Calc.Display, this.value)'></td>
        </tr>
      </table>
    </form>
  </body>
</html>