std::string? System::String? char*? wchar_t*?
// std::string
std::istringstream istr;
istr << this->textBox1->Text << "." << count;
this->textBox1->Text = istr.str();
// System::string
this->textBox1->Text += ".";
this->textBox1->Text += Convert::ToString(count);
// char* - assuming it's big enough
sprintf(this->textBox1->Text, "%s.%d", this->textBox1->Text, count);