if conditon:
    代码块
    condition必须是一个bool类型，这个地方有一个隐式转换bool（condition）

代码块：
    类似于if 语句的冒号后面的就是一个语句块
    在if、for 、def、class等关键字后使用代码块

if...elif...else语句
if condition1:
    代码块1
elif condition2:
    代码块2
elif condition3:
    代码块3
......
else:
    代码块

score = -1
if score < 0 :
    print(‘error input‘)
elif score <= 100:
    print(‘right score‘)
elif score == 0:
    print(‘zero‘)
else:
    print(‘please check it right‘)

if score < 0:
    print(‘error input‘)
else:
    if score == 0:
        print(‘zero‘)
    elif score <= 100:
        print(‘right score‘)
    else:
        print(‘input too big‘)

语法
while condition:
    block
当条件满足即condition为True，进入循环体，执行block
示例：计算1+2+3...+10 = ?
sum = 0
flag=10
while flag:
    sum += flag
    flag -= 1
print(sum)
#九九乘法表

i = 1
while i < 10:
    j = 1
    while j < 10:
        if i >= j:
            print(‘{} * {} = {}‘.format(i,j,i*j),end=‘\t‘)
        j += 1
    i += 1
    print()

for i in range(1,10):
    print(i)

#打印奇数
for i in range(1,10):
    if i % 2 == 0:
        continue
    print(i)

count = 0
for i in range(0,100,7):
    count += 1
    if count > 10:
        break
    print(i)