流程控制之if...else

---单分支---

today_weather = "rain_day"

if today_weather == "rain_day":

　　print("带伞")

---双分支---

age = 18

if age >= 18:

　　print("已成年")

else:

　　print("未成年")

---多分支---

count = 20
if count >=60:
    print("及格")
elif count > 80:
    print("良")
elif count >90:
    print("优秀")
else:
    print("不及格")