python基本循环结构 python循环结构例题

一、while 循环

        while关键字后跟随的是一个循环条件判断，解释器首先判断while循环条件是否成立，若成立，则执行代码块，执行完毕后再次判断循环条件是否成立，若成立，则再次执行代码块，知道循环条件不成立，退出循环。

 （一）while语句执行过程

设置初始条件（计数器）
while 循环条件（判断 计数器 是否达到 目标次数）:
    条件满足，做的事情1
    条件满足，做的事情2
         ......
    根据题意处理条件（计数器+1）
循环条件不满足时，做的事情

eg：计算100以内的奇数和

sum = 0
n = 1   #理解为计数器
while n < 100: #判断 n（计数器）是否 小于100（目标次数）
    sum += n  #满足循环条件，进行求和
    n += 2  #根据题意处理条件（计数器+2）
print(sum)  #循环条件不成立时，输出sum

 PS：while也要严格缩进格式，与选择结构一样缩进表示层级关系

while语句中，break用于跳出当层循环，通常与if语句连用；continue是忽略当次迭代的后续代码，直接进入循环的下次迭代。

 break示例：

#判断一个数是否为素数（质数）
a = int(input("请输入一个数："))
b = 2
if a == 1:
	print("这个数不是素数")
elif a == 2:
	print("这个数是素数")
else:
	while a > b:
		if a % b == 0:
			print("这个数不是素数")
			break
		b += 1
	else:
		print("这个数是素数")

continue示例：

num = 1
while num < 10:   
    num += 1
    if num % 2 > 0:     # 非双数时跳过输出
        continue
    print("1~10内的双数为",num)        # 输出双数2、4、6、8、10

（二）while嵌套循环（双重循环）

 经典案例  1：打印直角三角形

layer = int(input("请输入要打印的行数:"))
index = 1
while index <= layer:
	j = 1 #每行*的个数
	while j <= index:
		print("*",end="")
		j += 1
	print()
	index += 1

 经典案例  2：打印九九乘法表

i = 1
while i <= 9:
	j = 1
	while j<=i:
		res = i * j
		if res < 10:
			print("%s x %s = %s "%(i,j,(i*j)),end="  ")
		else:
			print("%s x %s = %s "%(i,j,(i*j)),end=" ")
		j += 1
	print()
	i += 1

 二、for 循环

（一）for循环遍历

  1、for循环可以遍历任意可迭代对象（序列、集合以及数值列表）。

  2、break用于跳出当层循环，通常与if语句连用；continue是忽略当次迭代的后续代码，直接进入循环的下次迭代。

 （二）for in 语句执行过程

for 循环变量 in 遍历数据集：
    语句块（针对列表元素进行操作）   #注意缩进

 1、range()函数 —— 前闭后开

（1）range(x) —— 生成一个 

 区间内的“整数列表”。（2）range(x,y) —— 生成一个 

 区间内的“整数列表”。 （3）range(x,y,step) —— 生成一个 

 区间内的“整数列表”，数值的变化随step的值变化而变化，step的值默认为1。

 2、for嵌套循环

 经典案例 ：打印菱形

#第一种
layer = int(input("请输入你要打印的行数："))
#上半部分
for i in range(1,layer//2+2):   #前闭后开
	#计算空格的个数
	space_num = layer - i
	for j in range(0,space_num):
		print(" ",end="")
	#计算*个数
	star_num = 2*i-1
	for j in range(0,star_num):
		print("*",end="")
	print("")
#下半部分
for i in range(layer//2,0,-1):
	#计算空格的个数
	space_num = layer - i
	for j in range(0,space_num):
		print(" ",end="")
	#计算*个数
	star_num = 2*i-1
	for j in range(0,star_num):
		print("*",end="")
	print("")
#第二种
rows = int(input("请输入要打印的行数："))
for i in range(1,rows):#变量i控制行数
    #计算空格
    for j in range(rows - i):#3~1
        print(" ",end="")
    #计算“*”个数        
    for j in range(2 * i - 1):#1~7            
        if  j == 1 or j == 2 * i - 1:
        	print("*",end="")
        else:
        	print(" ")
    print ("")
   
    #菱形的下半部分
for i in range(rows):
    for j in range(i):
        print(" ",end="") 
    for j in range(2 * (rows - i) - 1):#5~1
        if  j == 1 or j == 2 * (rows - i) - 1:
        	print("*",end="")
        else:
        	print(" ")
    print ("")

 三、对应练习

三、循环语句（37~54）

Demo37

import random
a = int(random.uniform(0,100))
print("Guess a magic number between 0 and 100")
b = int(input("Enter your guess:"))
while b < a:
	print("Your guess is too low")
	b = int(input("Enter your guess:"))
	while b > a:
		print("Your guess is too height")
		b = int(input("Enter your guess:"))	
if b == a:
	print("Yes, the number is %s" %b)

Demo38

n1,n2 = eval（input("请输入两个整数："))
if n1 > n2:
	gcd = "1"
	k = 1
	while k <= n2:
		if n1 % k == 0 and n2 % k == 0:
			gcd = k
		k += 1
	print(gcd)
elif n1 == n2:
	print(n1)
else:
	gcd = "1"
	k = 1
	while k <= n1:
		if n1 % k == 0 and n2 % k == 0:
			gcd = k
		k += 1
	print(gcd)

Demo39

import random
num = 0
total = 1000000
for i in range(0,total):
	x = random.random() * 2 - 1    #random()---产生0~1之间的数
	y = random.random() * 2 - 1
	distance = (x ** 2 + y ** 2) ** 0.5
	if distance <= 1:
		num += 1
pi = num / total * 4
print(pi)

Demo40

positives = 0
negatives = 0
sum = 0
while True:
	a = int(input("Enter an integer, the input ends if it is 0:"))
	if a == 0:
		break;
	elif a < 0:
		negatives += 1
	else:
		positives += 1 
	sum += a
total = negatives + positives
average = sum / total
if total1 == 0:
	print("You didn't enter any number")
else:
	print("The number of positives is %s" %positives)
	print("The number of negatives is %s" %negatives)
	print("The total is %s" %sum)
	print("The average is %.2f" %average)

Demo41

a  = int(input("输入一个整数："))
i = 2
if a == 1:
	print(1)
elif a == 2:  
	print(1,2)  
else:
	while i < a:
		if a % i == 0:
			print(i ,end= ",")
			a //= i
		else:
			i += 1
	print(int(a))

Demo42

a = int(input("请输入你要打印的行数："))
for i in range(1,a + 1):
    for j in range(a,0,-1):
        if j <= i:
            print("%s " %j,end="")
        else:
        	print("  ",end="")
    for j in range(2,a+1):
        if j<=i:
            print('%s ' %j,end="")
    print("")

Demo43

#a
print("模式A")
for i in range(1,7):
        for j in range(1,7):
            if j<=i:
            	print('%s ' %j,end="")
        print("")

#b
print("模式B")
for i in range(6,0,-1):
    for j in range(1,7):
        if j <= i:
            print("%s " %j,end="")
    print("")

#c
print("模式C")
for i in range(1,7):
    for j in range(6,0,-1):
        if j <= i:
            print("%s " %j,end="")
        else:
        	print("  ",end="")
    print("")

#d
print("模式D")
for i in range(6,0,-1):
	a = 6 - i
	print("  " *a,end="")
	for j in range(1,7):
		if j <= i:
			print("%s " %j,end="")
	print("")

Demo44

a = int(input("请输入一个数："))
for i in range(0,a):
	for j in range(a - i,0,-1):
		print("",end="\t")
	for k in range(1,i + 1):
		print(2 ** (k - 1),end="\t")
	for j in range(i + 1,0,-1):
		print(2 ** (j - 1),end="\t")
	print("")

Demo45

count = 0
for num in range(2,1001):
	for j in range(2,num):
		if (num % j == 0):
			break;
	else:
		print(num,end="\t")
		count += 1
		if count % 8 == 0:
			print("")

Demo46

sum = 0
for j in range(10000,100001,10000):
	sum += 0
	for i in range(1,j+1):
		sum += ((-1) ** i + 1 ) / (2*i-1)
		PI = 4 * sum
	print("当i为%d时，PI为%.9f" %(j,PI))

Demo47

for j in range(10000,100001,10000):
	e = 1
	item = 1
	for i in range(1,j + 1):
		item *= i #item的阶乘 item = item *
		e += 1 / item
	print("i = %d 时， e = %.19f"%(j,e))

Demo48

for i in range(1,10001):
	sum = 0
	for j in range(1,i):
		if i % j == 0:
			sum += j
	if i == sum:
		print(i)

Demo49

import random
user_count = 0
com_count = 0
while True:
	user= int(random.uniform(0,2))
	com = int(input("scissor (0),rock (1),paper(2):"))
	win = user - com
	if win == -2 or win == 1:
		user_count += 1
		if user_count == 2:
			print("恭喜，你赢了！！！")
			break
	elif win == 2 or win == -1:
		com_count += 1
		if com_count == 2:
			print("很遗憾，电脑赢了！！！")
			break

Demo50

a = int(input("Enter a number(0: for end of input) :"))
max = 0
count = 0
total = 0
while a != 0:
	if a >= max:
		max = a
		count += 1
	else:
		count -= 1
	a = int(input("Enter a number(0: for end of input) :"))
print("The largest number is %s"%max)
print("The occurrence of the largest number is %s"%count)

Demo51

num = int(input("请输入一个数："))
a = ""
while num != 0:
	b = num % 2
	a = str(b) + a
	num = num // 2
print(a)

Demo52

a = int(input("请输入一个十进制整数："))		#bin二进制，oct八进制，hex十六进制
print("十六进制为{:x}".format(a,a,a,a))

Demo53

import random
total = 1000000
count = 0
for i in range(0,total):
	x = random.random() * 2 - 1
	y = random.random() * 2 - 1
	if -1 <= x <= 0 and -1 <= y <= 1:
		count += 1
	elif 0 <= x <= 1 and 0 <= y <= 1 and y / (1 - x) <= 1:
		count += 1
print("1000000个随机点落在奇数区域的概率是%.12f" %(count / total))

Demo54

count = 0
for year in range(2001,2101):
	if  year % 4 == 0 and year % 100!=0 or y % 400 ==0:
		print(year,end = " ")
		count += 1
		if count % 10 == 0:
			print()