using System;
class Better
{
    static void Main(string[] args)
    {
        int a, b, c, Num1, Num2, Num3, Num4,Num5;
        
        Console.WriteLine("请输入三个数：");
        a = Convert.ToInt32( Console.ReadLine());
        b = Convert.ToInt32( Console.ReadLine());
        c = Convert.ToInt32( Console.ReadLine());
        if (a > b)
        {
            Num1 = a;
        }
        else
        {
            Num1 = b;
        }
        if (c > Num1)
        {
            Num2 = c;
        }
        else
        {
            Num2 = Num1;
        }



        if (a < b)
        {
            Num3 = a;
        }
        else
        {
            Num3 = b;
        }
        if (c < Num3)
        {
            Num4 = c;
        }
        else
        {
            Num4 = Num3;
        }

        if (Num4 < a && a < Num2)
        {
            Num5 = a;
        }
        if (Num4 < b && b < Num2)
        {
            Num5 = b;
        }
        if (Num4 < c && c < Num2)
        {
            Num5 = c;
        }
        Console.WriteLine("排序为：");
        Console.WriteLine("{0}",Num4);
        Console.WriteLine("{0}",Num5);
        Console.WriteLine("{0}",Num2);
    }
}
为什么出现这种情况：使用了未赋值的局部变量“Num5”

if (Num4 < a && a < Num2)
        {
            Num5 = a;
        }
        if (Num4 < b && b < Num2)
        {
            Num5 = b;
        }
        if (Num4 < c && c < Num2)
        {
            Num5 = c;
        }
如果这三个条件都不满足,就不会进入到这三个if中去,则Num5不会被赋值,例如你输入了三个一样的数
 Console.WriteLine("{0}",Num5);那输出的时候就不知道该输出什么值了
Num4和Num2,由于有在if和else中赋值,就是无论如何都会被赋值,但Num5有可能不被赋值

楼上正解，要么你都加个if else 要么声明变量的时候附个初始值

是的

[ 本帖最后由 白5130 于 2013-4-28 17:48 编辑 ]

非常感谢，问题真的是这样的，因为我是刚学C#,所以很多都不懂，再次感谢您的指导