【python】入门学习（三）

for循环

for i in range():   #注意冒号 range中默认从0开始 或者从指定的数字开始 到给定数字的前一个数字结束 递增递减皆是如此

for循环提供变量的自动初始化

for i in range(10):
    print(i,end = ‘ ‘)
print()
for i in range(5,10):
    print(i,end = ‘ ‘)
print()
for i in range(10,0,-1):
    print(i, end = ‘ ‘)
print()

>>> ================================ RESTART ================================
>>>
0 1 2 3 4 5 6 7 8 9
5 6 7 8 9
10 9 8 7 6 5 4 3 2 1 

while循环：

需要自己初始化，可以包含一个else语句块

i = 0
while i < 10:
    print(i,end = ‘ ‘)
    i = i + 1
print()

当事先循环次数不确定时，无法用for循环 如：

#donesum.py
total = 0
s = input(‘input a number or "done":‘)
while s != ‘done‘:
    total = total + int(s)
    s = input(‘input a number or "done":‘)
print(‘the total is ‘ + str(total))

break   #跳出循环

continue  #进入下一次循环  少用较好

多层循环：

#timestable.py
for row in range(1,10):
    for col in range(1,10):
        prod = row * col
        if prod < 10:
            print(‘ ‘, end = ‘‘)
        print(row * col, " ", end = ‘‘)
    print()

>>> ================================ RESTART ================================
>>>
 1   2   3   4   5   6   7   8   9
 2   4   6   8  10  12  14  16  18
 3   6   9  12  15  18  21  24  27
 4   8  12  16  20  24  28  32  36
 5  10  15  20  25  30  35  40  45
 6  12  18  24  30  36  42  48  54
 7  14  21  28  35  42  49  56  63
 8  16  24  32  40  48  56  64  72
 9  18  27  36  45  54  63  72  81