条件控制之while和for-创新互联

一。while 循环
    1.循环：重复做某件事

   2.语法
        while 条件：
        code1

   3.结束while的方式：
        1.条件不满足，下次循环开始时判断
        2.break直接结束本层循环

   4.while + continue
        continue 之后的代码不会运行了，直接开始下次循环
n= 0
while n < 6:
    if n == 4:
        n+=1
        continue
    else:
        print(n)
    n+=1

       
    5.while循环嵌套
        while:
            while:
                while:

       break
            break
                break
                
                
                
                
                
count = 1
tag = True
while tag:
    name = input("name: ")
    passwd = input("passwd ")
    if count == 3:
        print("too many")
        break
    if name == "chad" and passwd == "123":
        print("successfull")
        while tag:
            print("""
            1
            2
            3
            """)
            cho = input("choice:")
            if cho == "1":
                print(1)
            elif cho == "2":
                print(2)
            else:
                print(3)
                tag = False
    else:
        print("error")
        count +=1
                
    
    
    6. while + else
        如果while循环没有被break打断，才会执行
        循环要正常结束
count = 0
while count < 3:
    print(count)
    count += 1
else:
    print("run")

二。for  循环
    循环取值简洁
        for+brek
        for+continue
        for+else

   dic = {"name":"sdfa","age":23}
    for i in dic:
        print(i,dic[i])
    返回字符串

   dic = {"name":"sdfa","age":23}
    for i,r in dic.items():
        print(i,r)
    以字符串返回key和value

   dic = {"name":"sdfa","age":23}
    for i in dic.items():
        print(i)
    以元组返回key和value，一对key，value是一个元组

range(起始，结束，步长)
取头不取尾

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