C++类的定义问题。。。。 - 编程论坛

我听说类一般声明在.h文件中。定义在cpp文件中。于是我写了这样一个类和这样一个头文件
但是编译的时候说cpp文件内有语法错误。。。我不是很懂C++语法，大家帮我看一下这两个文件哪里的语法错了

===================错误内容========================
In file included from digclass.cpp:6:0:
digclass.h:17:31: 错误：为构造函数指定返回值无效
digclass.cpp:78:6: 错误：‘ShowDig’未声明
digclass.cpp: 在函数‘void DigClass(int)’中:
digclass.cpp:83:17: 错误：‘up’在此作用域中尚未声明
digclass.cpp:86:17: 错误：‘middle’在此作用域中尚未声明
digclass.cpp:97:17: 错误：‘down’在此作用域中尚未声明
digclass.h:17:31: 错误：为构造函数指定返回值无效

==============================cpp文件===================================

程序代码：

/*

*Filename:      digclass.cpp

*Created:      2011年09月29日 21时19分53秒

*Author:      thlgood

*/
#include "digclass.h"
#include <stdio.h>
#include <stdlib.h>
#include <string.h>

DigClass::DigClass(const char Num)
{

#ifdef _DEBUG_
    cout << "please input num without other character\n";
    exit (1);
#endif
    switch (Num)
    {
        case '0':
            strcpy(up, " _ ");
            strcpy(middle, "| |");
            strcpy(down, "|_|");
            break;
        case '1':
            strcpy(up, "   ");
            strcpy(middle, "  |");
            strcpy(down, "  |");
            break;
        case '2':
            strcpy(up, " _ ");
            strcpy(middle , " _|");
            strcpy(down, "|_ ");
            break;
        case '3':
            strcpy(up, " _ ");
            strcpy(middle," _|");
            strcpy(down, " _|");
            break;

        case '4':
            strcpy(up, "   ");
            strcpy(middle, "|_|");
            strcpy(down, "  |");
            break;
        case '5':
            strcpy(up, " _ ");
            strcpy(middle, "|_ ");
            strcpy(down, " _|");
            break;
        case '6':
            strcpy(up, " _ ");
            strcpy(middle, "|_ ");
            strcpy(down, "|_|");
            break;

        case '7':
            strcpy(up, " _ ");
            strcpy(middle, "  |");
            strcpy(down, "  |");
            break;

        case '8':
            strcpy(up, " _ ");
            strcpy(middle, "|_|");
            strcpy(down, "|_|");
            break;

        case '9':
            strcpy(up, " _ ");
            strcpy(middle, "|_|");
            strcpy(down, " _|");
            break;
    }
}

void ShowDig::DigClass(const int n)
{
    switch(n)
    {
        case 1:
            printf("%s", up);
            break;
        case 2:
            printf("%s", middle);
            break;
#ifdef _DEBUG_
        case 3:
            printf("%s", down);
            break;
        default:
            printf("Error, Not UP, Not Middle, NOT DOWN!!\n");
            exit(2);
#else
        default:
            printf("%s", down);
#endif
    }
}

======================END================
=========================头文件=================================

程序代码：

/*

*       Filename:  DigClass.h

*    Description:  Nothing

*        Created:  2011年09月29日 21时16分40秒

*         Author:  thlgood,

*/
#ifndef _DITCLASS_H_
#define _DIGCLASS_H_

class DigClass
{
    private:
        char up[4];
        char middle[4];
        char down[4];
    public:
        void DigClass(const char Num);
        void ShowDig(const int n);
};

#endif

=====================END=======================
============================说明=============================
我之前是学C语言的，目前是C++初学者。
所以代码的风格明显和C比较接近。。不过不碍事的。只是帮我改一下语法错误就好了。
我的平台是GNU/Linux Gcc

谢谢各位