Simple calculator with regexp

calculator_with_regexp

def cal(expr)
  while(true)
    matched = /(\d+)(\*)(\d+)/.match(expr)    
    expr.gsub!(matched[0],"#{matched[1].to_i * matched[3].to_i}") if matched

    matched = /(\d+)(\/)(\d+)/.match(expr)
    return "Error!" if matched and matched[3] == "0"
    expr.gsub!(matched[0],"#{matched[1].to_i / matched[3].to_i}") if matched

    matched = /(\d+)(\+)(\d+)/.match(expr)    
    expr.gsub!(matched[0],"#{matched[1].to_i + matched[3].to_i}") if matched

    matched = /(\d+)(\-)(\d+)/.match(expr)    
    expr.gsub!(matched[0],"#{matched[1].to_i - matched[3].to_i}") if matched
    
    break unless matched
  end

  expr
end


def test(expr, expected)
  old = expr.clone
  actual = cal(expr)

  if actual == expected
    puts "[PASS] #{old} is #{actual}"
  else
    puts "[FAIL] #{old} expected #{expected} but #{actual}"
  end
end

test("4-2","2")
test("2+3","5")
test("3*4","12")
test("6/2","3")
test("3/0","Error!")
test("2+4*2","10")