c# - 当前上下文中不存在名称 "shape"

Question

专门做一个继承测试程序来根除诸如此类的问题。

类本身并不重要，问题出在 Main 上。

我在 if 语句之前尝试了“Shape shape = null”，但在 if 语句中使用“Circle shape”等引发了错误。

主要内容:

    string shapeType = "";
    double side = 0;
    while (true)
    {
      Console.WriteLine("What type of shape? - (cir/tri/sqr");
      shapeType = Console.ReadLine();
      Console.WriteLine("How long are the sides, or the radius?");
      side = Convert.ToDouble(Console.ReadLine());
      if (shapeType == "cir")
      {
        Circle shape = new Circle();
      }
      else if (shapeType == "tri")
      {
        Triangle shape = new Triangle();
      }
      else
      {
        Square shape = new Square();
      }

      // Code interacting with shapes.
    }

Answer 1

您在 if block 中声明形状，这意味着在该 block 结束后它不可用。

您需要先声明它，并将其声明为 Shape:

Shape shape = null;

if (shapeType == "cir")
{
    shape = new Circle();
}
else if (shapeType == "tri")
{
    shape = new Triangle();
}
else
{
    shape = new Square();
}

// … etc