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在学习python的循环语句时，老师经常会要求我们用循环语句打印出三角形或菱形，今天俺就来演示演示如何用*打印出图形。
1、首先来看看如何打印出等腰三角形（如图）：
layer = int(input("请输入HANG数：")) #输入行数
for i in range(1,layer+1): #用i表示每一行
num1 = layer - i #num1表示每一行中空格的数量
for j in range(num1): #通过for循环语句打印空格
print(" ",end="")
num2 = i*2-1 #num2表示每一行中的星号的数量
for j in range(num2): #通过for循环语句打印星号
print("*",end="")
print("") #这个语句表示换行
解释：打印等腰三角形需要理解它的图形规律，设i表示行数，每一行星号的个数就等于（i*2-1），每一行星号前面空格的个数就等于总行数减去i。知道了等腰三角形怎么打印，菱形也就很相似了。
2、打印出菱形（如图）：
layer = int(input("请输入打印的奇数行数："))
while layer%2==0: #因为打印菱形要上下对称，所以行数要单数
layer = int(input("必须是奇数,请输入重新打印的行数："))
for i in range(1,(layer//2+2)):
num1 = layer//2+1 - i
for j in range(num1):
print(" ",end="")
num2 = 2*i-1
for j in range(num2):
print("*",end="")
print("")
for i in range((layer//2),0,-1) :
num1 = layer//2+1 - i
for j in range(num1):
print(" ",end="")
num2 = 2*i-1
for j in range(num2):
print("*",end="")
print("")
解释：以打印9行为例，前面5行和打印等腰三角形是一样的，后面四行与前面原理相同，只不过在range函数中是反着来的，数从大到小排。
3、打印出空心菱形（如图）：
layer = int(input("请输入奇数行数："))
while layer%2==0:
layer = int(input("不是奇数，请重新输入："))
for i in range(1,layer//2+2):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1: #判断是否打印第一个或最后一个星号
print("*",end= "")
else:
print(" ",end = "")
print("")
for i in range(layer//2,0,-1):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1:
print("*",end="")
else:
print(" ",end = "")
print("")
解释：要打印空心菱形，只需在打印星号时进行判断，如果是本行中第一个和最后一个星号就打印星号，否则就打印空格。
4、空心菱形中加入一行星号（如图）：
layer = int(input("请输入奇数行数："))
while layer%2==0:
layer = int(input("不是奇数，请重新输入："))
for i in range(1,layer//2+2):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1 or i == layer//2+1: #如果i的行数是中间那一行就全打印星号
print("*",end= "")
else:
print(" ",end = "")
print("")
for i in range(layer//2,0,-1):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1:
print("*",end="")
else:
print(" ",end = "")
print("")
5、空心菱形中加入十字架（如图）：
layer = int(input("请输入奇数行数："))
while layer%2==0:
layer = int(input("不是奇数，请重新输入："))
for i in range(1,layer//2+2):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1 or i == layer//2+1 or j == num2//2:
print("*",end= "")
else:
print(" ",end = "")
print("")
for i in range(layer//2,0,-1):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1 or j == num2//2:
print("*",end="")
else:
print(" ",end = "")
print("")
6、打印一棵树（如图）：
layer = int(input("请输入奇数行数："))
while layer%2==0:
layer = int(input("不是奇数，请重新输入："))
for i in range(1,layer//2+2):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j==0 or j == num2-1 or i == layer//2+1 or j == num2//2:
print("*",end= "")
else:
print(" ",end = "")
print("")
for i in range(layer//2,0,-1):
num1 = layer//2+1-i
for j in range(num1):
print(" ",end="")
num2 = i*2-1
for j in range(num2):
if j == num2//2:
print("*",end="")
else:
print(" ",end = "")
print("")
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