错误： ————————并非所有的代码路径都返回值。代码已在下面：

Question

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;namespace jicheng
{
    class Furniture
    {
        string colour;
        float height;
        float length;
        public Furniture(string a, float b, float c)
        {
            colour = a  ;
            height = b ;
            length = c ;
        }
        public string display1()
        {
            Console.WriteLine("颜色：{0}", colour );
        }
        public float display2()
        {
            Console.WriteLine("高度：{0}  长度：{1}",height,length  );
        }
    }
    class Bookshelf : Furniture
    {
        int shelf;
        public Bookshelf():base("红色",3.5f ,5.5f)
        {
            shelf = 5;
        }
        public int display3()
        {
            Console.WriteLine("层数：{0}", shelf);
        }
    }
    class Chair : Furniture
    {
        int leg;
        public Chair():base("黄色",1.0f,0.5f)
        {
            leg = 3;
        }
        public int display4()
        {
            Console.WriteLine("腿数：{0}", leg);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            Bookshelf obj = new Bookshelf();
            obj.display1();
            obj.display2();
            obj.display3();
            Chair my = new Chair();
            my.display1();
            my.display2();
            my.display4();
            Console.ReadLine();        }
      
    }
}

Answer 1

using System; 
using System.Collections.Generic; 
using System.Linq; 
using System.Text; namespace jicheng 
{ 
    class Furniture 
    { 
        string colour; 
        float height; 
        float length; 
        public Furniture(string a, float b, float c) 
        { 
            colour = a  ; 
            height = b ; 
            length = c ; 
        } 
        public string display1() 
        { 
            Console.WriteLine("颜色：{0}", colour ); 
        }         
        public float display2() 
        { 
            Console.WriteLine("高度：{0}  长度：{1}",height,length  ); 
        }     } 
    class Bookshelf : Furniture 
    { 
        int shelf; 
        public Bookshelf():base("红色",3.5f ,5.5f) 
        { 
            shelf = 5; 
        } 
        public int display3() 
        { 
            Console.WriteLine("层数：{0}", shelf); 
        }     } 
    class Chair : Furniture 
    { 
        int leg; 
        public Chair():base("黄色",1.0f,0.5f) 
        { 
            leg = 3; 
        } 
        public int display4() 
        { 
            Console.WriteLine("腿数：{0}", leg); 
        }     } 
    class Program 
    { 
        static void Main(string[] args) 
        { 
            Bookshelf obj = new Bookshelf(); 
            obj.display1(); 
            obj.display2(); 
            obj.display3(); 
            Chair my = new Chair(); 
            my.display1(); 
            my.display2(); 
            my.display4(); 
            Console.ReadLine();         } 
      
    } 
} 红色标注部分的代码都有问题，你的确没有返回值！你既然申明了类型就要返回return，否则请换用void表示无返回
 
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Answer 2

你的display()方法返回类型改为void就可以了,否则是必须都有返回值的，Console.WriteLine只是输出到控制台，不给方法提供返回值。