segmentation fault ..... in function const char nstrcat( char* des,... )

const char* nstrcat(char* des, ...){
      
   char* s;
   va_list vargs;
   va_start(vargs, des);

    while(s = va_arg(vargs, char*))
    {
        for(; *s; s++)
       {
          *des = *s;
            des++;
       }
    }
        *des = 0;
        va_end(vargs);
        return des;
}


Can anybody help to solve this?????