Error a function-definition is not allowed here before ‘{‘ token

void main1()    
{

    const int MAX = 50;

    class infix
    {

    private:

            char target[MAX], stack[MAX];
            char *s, *t;
            int top, l;
        public:
            infix( );
            void setexpr ( char *str );
            void push ( char c );
            char pop( );
            void convert( );
            int priority ( char c );
            void show( );
    };
    void infix :: infix( ) //error
    {
        top = -1;
        strcpy ( target, "" );
        strcpy ( stack, "" );
        l = 0;
    }
    void infix :: setexpr ( char *str )//error
    {
        s = str;
        strrev ( s );
        l = strlen ( s );
        * ( target + l ) = '\0';
        t = target + ( l - 1 );
    }
    void infix :: push ( char c )//error
    {
        if ( top == MAX - 1 )
            cout << "\nStack is full\n";
        else
        {
            top++ ;
            stack[top] = c;
        }
    }
}

I am having trouble with this code. This is a part of my code for infix to prefix converter. My compiler keeps giving me the error:

“A function-declaration is not allowed here – before ‘{‘ token”

There’s actually three errors in this project. My project is due in September 2015, so please help! Thanks in advance.