text: var firstDigit = '';
  var secondDigit = '';
  var currentOperator = '';
  var isSecondDigit = false;
  
  const screen = document.querySelector('.txtScreen');
  
  function insertNumber(num) {
      if (screen.innerText.length < 15) {
          if (currentOperator.length > 0) {
              isSecondDigit = true;
              secondDigit += num;
  
              if (secondDigit.length <= 0) {
                  clearScreen();
              }
  
              screen.innerText += num;
          }
          else {
              firstDigit += num;
              screen.innerText += num;
          }
      }
      else return
  }
  
  function insertOperator(operator) {
      currentOperator = operator;
  
      clearScreen();
  }
  
  function insertReset() {
      firstDigit = '';
      secondDigit = '';
      currentOperator = '';
      isSecondDigit = false;
  
      clearScreen();
  }
  
  function clearScreen() {
      screen.innerText = '';
  }
  
  function insertResult() {
      if (isSecondDigit) {
          const strToNumberFisrtDigit = Number(firstDigit);
          const strToNumberSecondDigit = Number(secondDigit);
  
          let calc = null;
  
          switch (currentOperator) {
              case '+':
                  calc = strToNumberFisrtDigit + strToNumberSecondDigit;
                  break;
              case '-':
                  calc = strToNumberFisrtDigit - strToNumberSecondDigit;
                  break;
              case '*':
                  calc = strToNumberFisrtDigit * strToNumberSecondDigit;
                  break;
              case '/':
                  calc = strToNumberFisrtDigit / strToNumberSecondDigit;
                  break;
              case '%':
                  calc = strToNumberFisrtDigit % strToNumberSecondDigit;
                  break;
              default:
                  window.alert('Operador Inválido');
          }
  
          screen.innerText = calc;
      }
      else return
  }