一、引子
1、什么是循环?
循环就是重复做某件事
2、为何要有循环
为了控制计算机能够像人一样去重复做某件事
3、如何用循环
基本语法:
while 条件:
代码1
代码2
代码3
二、while循环的基本用法
例:
i=0
tag=True
while tag:
if i==5
tag=false
print(i)
i+=1
i=0
while i<6
print(i)
i+=1
三、死循环:条件永远为True
例如:1+1
CPU如果参与计算的循环,将会占用CPU的性能,造成伤害
四、结束while循环的两种方式
方式一:把条件改为False
特点:等到本次循环体代码运行完毕后,下一次循环判断条件时才会生效
例如:
i = 0 tag = True while tag: if i == 5 : tag = False print(i) i+=1
方式二、break代表结束本层循环
特点:立即干掉本层的while循环
i = 0 tag = True while tag if i == 5: tag = False print(i) i+=1
四、嵌套多层的while循环
方式一:
tag = True while tag: while tag: while tag: tag = false
方式二:
while True: while True: while True: break break break
五、案例
username = 'egon' password = '123' tag = True while tag <= 3: inp_name = input('请输入您的账号:') inp_pwd = input('请输入您的密码:') if inp_name == username and inp_pwd == password: print('登录成功') while True: print(""" 0 退出 1 存款 2 取款 3 转账 """) count = input("请选择您的业务") if count == "0": break elif count == "1": print('正在存款中。。。') elif count == "2": print('正在取款中。。。') elif count == "3": print('正在转账中。。。') print('谢谢您的使用,再见') else: print('账号名或密码错误') tag += 1 if tag == 4: print("你没了")
六、while+continue
结束本次循环,直接进入下次
count = 0 while count < 6: if count == 2 or count == 4: # break count += 1 continue # continue同级别之后千万别写代码,写了也不会运行 print(count) count += 1
七、while+else:的子代码块会在while循环正常死亡时运行,没被break干掉的叫正常死亡
count = 0 while count < 5: if count == 2: # count += 1 # continue break print(count) count += 1 else: print('====>')
八、for循环
1、基本用法:
for x in names: print(x) dic={"k1":111,'K2':2222,"k3":333} for x in dic: print(x,dic[x]) for x in "hello": print(x) for x,y in [["name","egon"],["age",18],["gender","male"]]: # x,y = ['name', 'egon'] print(x,y)
2、for+break
for i in [11,22,33,44,55]: if i == 33: break print(i)
3、for+continue
for i in [11,22,33,44,55]: if i == 33: continue print(i)
4、for+else
for i in [11,22,33,44,55]: if i == 33: break print(i) else: print('++++++++>')
5、range
i=0 while i < 3: print(111) print(222) print(333) i+=1 for x in range(3): print(111) print(222) print(333)