# if
score = 88

if score>=90 and score<=100 :
 print("优")
elif score<=90 and score>=80 : # else if
 print("中")
else :
 print("差")

# while
count = 0
while count<5 :
 # continue中止本次循环
 # 下面语句会导致永远循环
 # if count == 1:
 # continue
 print('hello')
 count = count + 1

 # break中止循环
 if count==3 :
 break

else :
 print('exit while')

# for
lst = ['baidu', 'alibaba', 'tencent']
for value in lst :
 print(value)

for i in range(5) :
 print(i)

for i in range(7,0,-1):
 print(i)

# 习题 1
score = 55
if score >= 90 and score <= 100 :
 print("优秀")
elif score >= 80 and score < 90 :
 print("良好")
elif score >= 70 and score < 80 :
 print("中等")
elif score >= 60 and score < 70 :
 print("及格")
else :
 print("不及格")

# 习题2
for i in range(7,0,-1) :
 star = ''
 for j in range(i) :
 star = star + '*'
 print(star)

for i in range(7,0,-1) :
 star = '*'
 print(star*i)