1. The simplest answer is

     apstring JoinStrings( apstring, apstring, apstring, apstring );

An alternative is to provide parameters, as in

     apstring JoinStrings( apstring first, apstring second,
                           apstring third, apstring fourth );

2. The simplest solution is:

     apstring JoinStrings( apstring first, apstring second,
                           apstring third, apstring fourth )
     {
         apstring result;
         result = first + "*" + second + "*" + third + "*" + fourth;
         return result;
     }

Alternative function bodies (one line instead of three) are:

         return first + "*" + second + "*" + third + "*" + fourth;

         return first + '*' + second + '*' + third + '*' + fourth;

3. Here is a simple main program.

     #include <iostream.h>
     #include "apstring.h"

     /* Include the function declaration and definition from parts 1 and 2 here */

     int main( )
     {
         apstring first, second, third, fourth;
       
         cout << "Enter four strings: " << endl;
         cin  >> first >> second >> third >> fourth;

         cout << "The result is "
              << JoinStrings( first, second, third, fourth ) << endl;

         return 0;
     }