（十一）if...else&for循环&while循环

----------------------------------if   else------------------------------
1.最基本的if语句：
if name =="Alex":#注意缩进
    print("so handsome")#可以结束,没问题.
#继续加条件：
elif name =="oldboy":
    print("too old")
else:#代表上面的条件都不成立走这个
    print"goodboy!"
2.猜年龄：
oldboy_age = 39
guess_age =int(input("age:"))#str--->int
print(type(guess_age))
if guess_age ==oldboy_age:
    print("correct!!")
elif guess_age > oldboy_age:#else if
    print("try smaller!!")
else:
    print("try bigger!!")
3.猜成绩：
score = int（input（"输入你的成绩:"））
if score >100:
    print("滚")
elif score == 100:
    print("A+")
elif score >=80:
    print("B")
elif score >=60:
    print("C")
elif score >=40:
    print("C-")
else:
    print("D")
if----else----只走一个逻辑,从上到下!
-------------------------------for--------------------------------
1.最简单的for循环
for i in range (10):#这句话的意思就是我要去循环这一组数据[0,1,2,3,4,5,6,7,8,9]这组数据中循环,每循环一次就拿出一个值来打印                    
#range其实就是一组数据    print(i)       
#i就相当于一个临

2.猜年龄

 2.1 break 猜对了及时跳出循环
 2.2 3次结束以后失败了!不能打印最后一句"Welcome to 2 level!"
 2.3 只有猜对了,才能打印这句话
 2.4怎么退出程序?exit()
 2.5 怎么使用for---else，
oldboy_age = 39
for i in range (3):-------------------------------for下面的内容都会循环.
    guess_age =int(input("age:"))#str--->int
    print(type(guess_age))
    if guess_age ==oldboy_age:
        print("correct!!")
        break-------------------------------------猜对了就跳出循环！
    elif guess_age > oldboy_age:#else if
        print("try smaller!!")
    else:
        print("try bigger!!")
else：#如果for循环正常结束,中间没有被break,代表猜错了.上面不成立!
    exit("too many attempts!")
print ("welcome to 2 level!")

3.嵌套循环：
3.1简单嵌套:
for i in range (10):
    for j in range (10):
    print(i,j)
3.2 j >5:
for i in range (10):
    for j in range (10):
    print(i,j) #先打印后判断,打印出来会有6，除非把这个写在if后面就没有6
    if j>5:
break#-------------只是跳出当前循环;
3.3 j<5,不打印,j>5,才打印------continue
for i in range (10):
    for j in range (10):
    if j<5:----------------大循环走了10次，小循环没走，直接跳出
    break  ----------------直接跳整个当前层循环,什么都没打印
    print(i,j)
不能用break,用continue
for i in range (10):
    for j in range (10):
    if j<5:
        continue
        print(i,j)
4.用户登陆:
user = "gaojun"
password ="123abc"
for i in range(3):
    user = input('请输入用户名：')
    password  = input('请输入密码:')
    if  user == "gaojun" and password =="123abc":
        print("欢迎！gaojun！")
        break
    else:
        print("用户或密码错误！")
else:
    print("输入次数到达3次，请稍后再试！")

-------------------------while--------------------------

1.最简单的while循环:
count = 0#定义count变量,为了让你看到循环了多少次
while True:#条件为真,True永远为真
    print("you are a good boy!",count)
    count +=1
2.上面的例子,跳出死循环:
count = 0
while True:
    if count = 1000000
        print("you are a good boy!",count)
        break
    count +=1
3.其他办法施行运行100次就退出;
count = 0
while count<100:
    print("you are a good boy!",count)
    count +=1
4.猜年龄----
4.1输入空值会报错怎么解决?isdigit
4.2怎么限制次数 count<3  count+=1
count = 0
oldboy_age = 56
while count <3:
    guess_age =input("gae>>:")
    if guess_age.isdigit():
        guess_age = int(guess_age)
    else:
        continue
    if guess_age == oldboy_age:
        print("猜对了！")
        break
     elif guess_age >oldboy_age:
        print("往小里猜！")
      else:
        print("往大猜！")
     count+=1