sub middleThreeDigits$ (n)
    if n < 0  n = -n
    if n < 100  return ""  // error code
    if n < 1000  return str$(n)
    if n < 10000  return ""
    ns$ = str$(n)
    if mod(len(ns$), 2) = 0  return ""  // need to have an odd number of digits for there to be 3 middle
    return mid$(ns$, len(ns$) / 2, 3)
end sub

dim a(16)
a(0) =       123 : a(1) = 12345  : a(2) = 1234567
a(3) = 987654321 : a(4) = 10001  : a(5) = -10001
a(6) =      -123 : a(7) = -100   : a(8) = 100
a(9) = -123451
a(10) =        2 : a(11) = -1    : a(12) = -10
a(13) =     2002 : a(14) = -2002 : a(15) = 0

print "The 3 middle digits of the following numbers are : \n"

for i = 1 to 16
    result$ = middleThreeDigits$(a(i))
    print a(i), "\t => ";
    if result$ <> "" then
        print result$
    else
        print "Error: does not have 3 middle digits"
    fi
next