程序的控制结构

程序的分支结构:

单分支结构:

guess = eval(input( ))
if guess==99:
print("猜对")

Snipaste_2020-07-16_21-29-48.png

二分支结构:

guess = eval(input( ))
if guess==99:
print("猜对了")
else:
print("猜错了")

Snipaste_2020-07-16_21-31-15.png

#紧凑形式:
guess = eval(input( ))
print("猜{}了".format("对"if guess == 99 else"错"))

多分支结构:

guess = eval(input( ))
if guess>99:
print("猜错了")
elif guess<99:
print("猜错了")
else:
print("猜对了")

------

条件判断及组合:

guess = eval(input( ))
if guess>99 or guess<99:
print("猜错了")
else:
print("猜对了")

guess = eval(input( ))
if guess != 99:
print("猜错了")
else:
print("猜对了")

程序的异常处理:

Snipaste_2020-07-17_18-44-06.png

Snipaste_2020-07-17_18-47-15.png

身体质量指数BMI:

height，weight = eval(input( "请输入身高(米)和体重(公斤)[用逗号隔开]:"))
BMI = weight/pow(height,2)
print("BMI数值是{:.2f}".format(BMI))
who,nat = " "," "
if BMI < 18.5:
print("偏瘦","偏瘦")
elif 18.5<= BMI < 24:
print( "正常","正常")
elif 24<= BMI < 25:
print( "偏胖","正常")
elif 25<= BMI <28:
print( "偏胖","偏胖")
elif 28<= BMI < 30:
print( "肥胖","偏胖")
else :
print("肥胖","肥胖")
print("BMI指标为国内'{0}',国际'{1}'".format(who,nat))

程序的循环结构:

循环控制保留字break和continue：

Snipaste_2020-07-24_16-47-58.png

Snipaste_2020-07-24_16-52-27.png

Snipaste_2020-07-24_16-54-20.png

一个break只能跳出最内层循环，且只能跳出一层循环。

Snipaste_2020-07-24_16-54-53.png

循环的扩展：

循环与else：

for <循环变量> in <遍历结构>:
  <语句块1>
else:
  <语句块2>

while (条件):
  <语句块1>
else:
  <语句块2>

当循环没有被break退出时，执行else语句块
else语句块作为“正常”完成循环的奖励
这里的else用法和程序异常处理的else用法相似

random库的使用:

Snipaste_2020-07-24_17-22-53.png

Snipaste_2020-07-24_17-24-46.png

扩展随机数函数.png

圆周率的计算实例:

公式法

pi=0
for i in range(100):
    pi += 1/pow(16,i)*(\
        4/(8*i+1)–2/(8*i+4)–\
        1/(8*i+5)–1/(8*i+6))
print("圆周率的近似值是:{:.9f}".format(pi))

蒙特卡洛法:

from random import random
from time import perf_counter
darts =1000*1000
hits = 0
start = perf_counter()
for i in range(0,darts):
    x,y=random(),random()
    dist = pow(x**2+y**2,0.5)
    if dist <= 1:
        hits += 1
print("圆周率的近似值是:{}".format(pi))
print("运行时间是:{:.5f}s".format(perf_counter()–start))

Snipaste_2020-07-24_19-17-19.png

圆周率的计算.png

Snipaste_2020-07-24_22-54-50.png