replace_first_digit_reg_exp.rb

def replaceFirstDigitRegExp(input)
    x = 0
    string = ""
    change = false
    while (x < input.length)
          if input[x] >= '0' and input[x] <= '9' and change == false then
             string[x] = "#"
             change = true
          else
             string[x] = input[x]
          end

         x = x + 1
    end

    return string
end