if 及循環語句

 1. if 語句

• if語句支持嵌套
• 當代碼塊不想執行任何內容時，需用pass占位

if 條件:
　　代碼塊
else:
　　代碼塊

if 條件:
　　代碼塊
elif 條件:
　　代碼塊
else:
　　代碼塊

if 1==1:
    if 2==2:
        print('Hello')
    else:
        print('welcome')
else:
    print('bye')

if 1==1:
    pass
else:
    print('hello')

 2. while循環語句

# 死循環
import time

while 1==1:
    print('OK',time.time())
#--------------------------------------------

import time

count = 0

while count < 10:
    print('OK',time.time())
    count += 1
print(123)
#--------------------------------------------

count = 0
while count < 10:
    print(count)
    count += 1
else:
    print('else')
print('...')

 

# 使用while循環輸入1 2 3 4 5 6    8 9 10

count = 1
while count < 11:
    if count != 7:
        print(count,end=' ')
        count += 1
    else:
        print(' ',end=' ')
        count += 1
# -------------------------------------------------

# 求1-100的所有數的和

s = 0
count = 0
while count < 100:
    count +=1
    s += count
print(s)
# -------------------------------------------------

# 輸出1-100內的所有奇數

count = 1
while count <= 100:
    if count%2 != 0:
        print(count, end=' ')
    count += 1
# -------------------------------------------------

#輸出1-100內的所有偶數

count = 1
while count <= 100:
    if count%2 ==0:
        print(count, end=' ')
    count += 1
# -------------------------------------------------

#求1-2+3-4+5...99的所有數的和

count = 0
s1 = 0
s2 = 0
while count < 99:
    count += 1
    if count%2 !=0:
        s1 += count
    else:
        s2 += count
print(s1-s2)

# 即就是：
count = 1
s = 0
while count < 100:
    if count%2 !=0:
        s += count
    else:
        s -= count
    count += 1
print(s)
# -------------------------------------------------

#用戶登錄（三次機會重試）

count = 0
while count < 3:
    user = input('請輸入用戶名：')
    pwd = input('請輸入密碼：')
    if user == 'root' and pwd == 'root':
        print('歡迎登錄')
        break
    else:
        if count != 2:
            print('用戶名或密碼輸入有誤，請重新輸入，若連續輸入錯誤3次，今日將鎖定賬戶')
        else:
            print('連續輸入錯誤3次，賬戶已鎖定')
    count += 1

3. for循環語句

for 變量名 in 字符串
    代碼塊

4. break和continue

• continue，終止當前循環，開始下一次循環
• break，終止所有循環

count = 0
while count < 10:
#當count等於7時，執行continue終止當前循環，不再執行后面的print和count+=1，直接回到while開頭開始下一次循環
    if count == 7:
        count += 1
        continue
    print(count)
    count += 1
# -------------------------------------------------

count = 0
while count < 10:
    count += 1
    print(count)
    break
    print(111)
print('end')
#結果為1和end，遇到break終止所有循環，不會執行print(111)，直接跳出循環向下繼續執行
# -------------------------------------------------

test = '朝辭白帝彩雲間'

for item in test:
    print(item)
    break
# 朝

for item in test:
    continue
    print(item)
# 什么也不輸出