条件、循环、函数定义练习

1. 注意标准库的两种导入与使用方式，建议大家采用<库名>.<函数名>的方式。
2. 对前面的代码进行优化，用for,while,if,def实现：
   1. 画五角星

      import turtle
      turtle.fillcolor("green")
      
      turtle.begin_fill()
      for i in range(5):
         turtle.forward (180)
         turtle.right(144)
      turtle.end_fill()
         
      turtle.hideturtle()

      

       

   2. 画同心圆

      import turtle
      turtle.speed(10)
      
      for i in range(5):
          turtle.up ()
          turtle.goto(0,-20*(i+1))
          turtle.down()
          turtle.circle(20*(i+1))

      

       

   3. 画太阳花

      import turtle
      turtle.speed (10)
      turtle.fillcolor ("yellow")
      
      turtle.begin_fill ()
      while True:
          turtle.forward(194)
          turtle.left(170)
          if(abs(turtle.pos()))<1:
            break
      turtle.end_fill ()
      
      turtle.hideturtle()

      

       

   4. 画五个五角星

      import turtle
      turtle.speed(10)
      turtle.bgcolor ("red")
      turtle.color("yellow")
      turtle.fillcolor("yellow")
      turtle.begin_fill()
      
      def it_goto(x,y):
         turtle.up()
         turtle.goto(x,y)
         turtle.down()
      
      def it_star(a):
         for i in range(5):
               turtle.forward(a)
               turtle.right(144)
               
      def it_left(b):
         turtle.left(b)
      
      turtle.begin_fill() 
      it_goto(-350,180)
      it_star(150)
      turtle.end_fill()
      
      turtle.begin_fill()
      it_goto(-150,250)
      it_left(50)
      it_star(40)
      turtle.end_fill()
      
      turtle.begin_fill()
      it_goto(-100,170)
      it_left(50)
      it_star(40)
      turtle.end_fill()
      
      turtle.begin_fill()
      it_goto(-105,85)
      it_left(45)
      it_star(40)
      turtle.end_fill()
      
      turtle.begin_fill()
      it_goto(-150,35)
      it_left(50)
      it_star(40)
      turtle.end_fill()
      
      turtle.hideturtle()

      

       

   5. 画◇花瓣的太阳花。

      import turtle
      turtle.speed (10)
      turtle.fillcolor("orange")
      turtle.pencolor("brown")
      turtle.begin_fill()
      
      for i in range(37):
              turtle.forward(100)
              turtle.right(60)
              turtle.forward(100)
              turtle.right(120)
              turtle.forward(100)
              turtle.right(60)
              turtle.forward(100)
              turtle.right(130)       
      turtle.end_fill()
      turtle.right(80)
      turtle.forward(300)
      turtle.hideturtle()