title: bash - Integer expression expected
body: <p>I wanted to simulate a vending machine where you can buy things only if you throw 2€ inside.</p>
  
  <p>It works as long as i only enter integer values, but if i enter a character or a float it suddenly stops to work. And throws an error that there is an integer expression expected. </p>
  
  <pre><code>read -p "Throw in money" x
  echo ""
  
  while [ $x -ne 2 ] ;
  do
  case $x in
          0.5)
                  read -p "more money" z
                  x=$(($x + $z))
                  ;;
          1)
                  read -p "more money" z
                  x=$(($x + $z))
                  ;;
          1.5)
                  read -p "more money" z
                  x=$(($x + $z))
                  ;;
          "R")
                  echo "return x"
                  x=0
                  ;;
          ?)
                  echo "enter something else!"
                  x=0
                  ;;
  esac
  done
  </code></pre>