Task

Write a function/procedure/subroutine that is called with an integer value and returns the middle three digits of the integer if possible or a clear indication of an error if this is not possible.

Note: The order of the middle digits should be preserved.

Your function should be tested with the following values; the first line should return valid answers, those of the second line should return clear indications of an error:

123, 12345, 1234567, 987654321, 10001, -10001, -123, -100, 100, -12345
1, 2, -1, -10, 2002, -2002, 0

Show your output on this page.




proc middleThree n {
    if {$n < 0} {
	set n [expr {-$n}]
    }
    set idx [expr {[string length $n] - 2}]
    if {$idx % 2 == 0} {
	error "no middle three digits: input is of even length"
    }
    if {$idx < 1} {
	error "no middle three digits: insufficient digits"
    }
    set idx [expr {$idx / 2}]
    string range $n $idx [expr {$idx+2}]
}