FtoC version 1

#!/usr/bin/sh

function FtoC
{
    fahr=$1
    (( x = fahr - 32 ))
    (( y = ( 10 * x ) / 18 ))
    return $y
}

while true
do
    print "enter the F:"
    unset fahr
    read fahr
    typeset -i fahr
    FtoC $fahr
    print "$fahr in F is $? in C"
done
   

FtoC version 2

#!/usr/bin/sh

function FtoC
{
    fahr=$1
    (( x = fahr - 32 ))
    (( y = ( 10 * x ) / 18 ))
    return $y
}

while true
do
    print "enter the F:"
    read fahr

    if [ $fahr == 'q' ]
    then
        break
    fi

    typeset -i fahr
    FtoC $fahr
    print "$fahr in F is $? in C"
done