text: var num, acc = 0,
      op = "";
  
  function mas() {
      "use strict";
      acc = num.value;
      op = "+";
  }
  
  function menos() {
      "use strict";
      acc = num.value;
      op = "-";
  }
  
  function multiplicar() {
      "use strict";
      acc = num.value;
      op = "*";
  }
  function dividir() {
      "use strict";
      acc = num.value;
      op = "/";
  }
  function x_y() {
      "use strict";
      acc = num.value;
      op = "xy";
  }
  function x2() {
      "use strict";
      acc = num.value;
      op = "x2";
  }
  function x1() {
      "use strict";
      acc = num.value;
      op = "_1x";
  }
  function raiz() {
      "use strict";
      acc = num.value;
      op = "sqrt";
  }
  function parte_entera() {
      "use strict";
      acc = num.value;
      op = "_pEntera";
  }
  
  function calcular() {
      "use strict";
      if (op === "+") {
          num.value = (+acc + (+num.value));
      }
      if (op === "-") {
          num.value = (+acc - (+num.value));
      }
      if (op === "*") {
          num.value = (+acc * (+num.value));
      }
      if (op === "/") {
          num.value = (+acc / (+num.value));
      }
      if (op === "xy") {
          num.value = Math.pow(+acc, +num.value);
      }
      if (op === "x2") {
          num.value = Math.pow(+acc, 2);
      }
      if (op === "_1x") {
          num.value = 1 / (+acc);
      }
      if (op === "sqrt") {
          num.value = Math.sqrt(+acc);
      }
      if (op === "_pEntera") {
          (acc > 0) ? (num.value = Math.floor(+acc)) : (num.value = -Math.ceil(+acc));
      }
  }
  
  function inic() {
      "use strict";
      num = document.getElementById("num");
  }
  
  function vaciar() {
      "use strict";
      num.value = "";
  }
  
  