OS Converter Exercise

#Author - MR
#Date modified - 1/29/14

until [ "$choice" == "3" ]
do
    echo "What do you want to convert?"
    echo "============================"
        echo "1. Celsius to Fahrenheit"
        echo "2. Fahrenheit to Celsius"
        echo "3. Exit"
        echo "============================"
        echo
        echo -n "Enter choice: "
        read choice
        echo


    fah_to_cel()
    {
            echo -n "Enter fahrenheit: "
            read fah
            a=32
            b=0.56
            echo -n "$fah FAHRENHEIT in CELSIUS is: "
            echo -n "$fah $a $b" | awk '{ print ($1-$2) * $3 }'
            echo
    }

    cel_to_fah()
    {
        echo -n "Enter celsius: "
            read cel
            c=1.8
            d=32
            echo -n "$cel CELSIUS in FAHRENHEIT is: "
            echo -n "$cel $c $d" | awk '{ print ($1*$2) + $3 }'
            echo
    }


    if [ "$choice" == "1" ]
    then
            fah_to_cel
    elif [ "$choice" == "2" ]
    then
            cel_to_fah
    elif [ "$choice" == "3" ]
    then
        echo "Goodbye"
    echo
        else
            echo "Invalid choice"
    fi

done