---

#!/bin/bash

while true; do
  read -r a op b
  if [[ -z $a ]]; then
    continue
  fi

  if [[ $a == "exit" ]]; then
    echo "bye"
    break
  fi

  if [[ -z $op || -z $b ]]; then
    echo "error"
    break
  fi

  case $op in
    "+")
      echo $((a + b))
      ;;
    "-")
      echo $((a - b))
      ;;
    "*")
      echo $((a * b))
      ;;
    "/")
      if [[ $b -eq 0 ]]; then
        echo "error"
        break
      fi
      echo $((a / b))
      ;;
    "%")
      if [[ $b -eq 0 ]]; then
        echo "error"
        break
      fi
      echo $((a % b))
      ;;
    "**")
      echo $((a ** b))
      ;;
    *)
      echo "error"
      break
      ;;
  esac
done