white. boards. suck.

strstr

def substring(haystack, needle)
  i = 0
  while i <= haystack.length
    if haystack[i,(needle.length)] == needle
      return i
    else
      i += 1
    end
    if i == haystack.length
      return nil
    end
  end
end

puts substring("stupid", "smart")
puts substring("stupid", "stu")
puts substring("stupid", "pid")