<!DOCTYPE html>
<html>
<head>
<title>Mi primera calculadora</title>
<meta charset="utf-8">

<script type="text/javascript">
  var num, acc = 0, op = "";
  var keyCode;
  var nombre = "";

  function mas()   			{ acc = num.value;  op = "+"; }
  function menos() 			{ acc = num.value;  op = "-"; }
  function multiplica()			{ acc = num.value;  op = "x"; }
  function divide()			{ acc = num.value;  op = "/"; }
  function cuadrado()			{ acc = num.value;  op = "x^2"; calcular()}
  function inverso()			{ acc = num.value;  op = "1/x"; calcular()}
  function raiz()				{ acc = num.value;  op = "Raíz 2"; calcular()}
  function parte_entera()		{ acc = num.value;  op = "Parte Entera"; calcular()}
  function x_elev_y()			{ acc = num.value;  op = "x^y"}

  function calcular() {
    if (op === "+") 			{num.value = (+acc + +num.value)}
    if (op === "-") 			{num.value = (+acc - +num.value)}
    if (op === "x") 			{num.value = (+acc * +num.value)}
    if (op === "/") 			{num.value = (+acc / +num.value)}
    if (op === "x^2") 			{num.value = (+acc * +acc)}
    if (op === "1/x") 			{num.value = (1 / +acc)}
    if (op === "Raíz 2") 		{num.value = (Math.sqrt(+acc))}
    if (op === "Parte Entera") 	{if(+acc>0)	(num.value = Math.floor(+acc)); else (num.value = Math.ceil(+acc));}
    if (op === "x^y") 			{num.value = (Math.pow(+acc,+num.value))}

  }

    function tecla(e){
    if(window.event)keyCode=window.event.keyCode;
    else if(e) keyCode=e.which;
    if(keyCode==13)
	calcular();
    }

  function inic () {
	num = document.getElementById("num");
	while(!nombre)
	nombre = prompt("Introduzca su nombre");
	alert("Hola "+nombre);
	document.getElementById("bienvenida").innerHTML = "Buenos días, bienvenido a la calculadora de " + nombre;
  }

  function vaciar () {num.value = "";}

</script>

</head>

<body onLoad="inic()" onkeypress="tecla(event)">

  <div id="bienvenida"></div>
  <p>
  <input type="text" size="12" id="num" onClick="vaciar()" autofocus><p>
  <button onClick="mas()">+</button>
  <button onClick="menos()">-</button>
  <button onClick="multiplica()">x</button>
  <button onClick="divide()">/</button><br>
  <button onClick="cuadrado()">x^2</button>
  <button onClick="inverso()">1/x</button>
  <button onClick="raiz()">Raíz 2</button><br>
  <button onClick="parte_entera()">Parte Entera</button>
  <button onClick="x_elev_y()">x^y</button>
  <button onClick="calcular()">=</button><br>
  </p>

</body>
</html>