[C/C++] Problem mit Programm

#include <iostream>
#include <fstream>
using namespace std;

class RamBufferedWrite
{
 
 
 public:
 // Funktionen
 void WriteToFile();
 void WriteToFile(char filename[]);
 void WriteToBuffer(char newstring[]);
 void ShowBuffer();
 
 private:
 void ChangeBufferSize(int pluslength);
 char Buffer[1];
 
 
};


void RamBufferedWrite::ChangeBufferSize(int pluslength)
{
 int oldlength = sizeof(Buffer);
 char Buffer[oldlength + pluslength];
}

void RamBufferedWrite::WriteToBuffer(char newstring[])
{
 //Startpunkt ermitteln
 int WritePosition = strlen(Buffer);
 // Arraygröße anpassen
 int pluslength = strlen(newstring);
 ChangeBufferSize(pluslength);
 // neuen inhalt hinzufügen
 for (int i = 0; i < pluslength; i++)
 {
 Buffer[WritePosition]=newstring[i];
 WritePosition++;
 }
 Buffer[WritePosition]= '\0';
}


void RamBufferedWrite::ShowBuffer()
{
 cout << "\n";
 cout << Buffer;
 cout << "\n";
}



void RamBufferedWrite::WriteToFile()
{
 WriteToFile("test.dat");
}

void RamBufferedWrite::WriteToFile(char filename[])
{
 fstream datei;
 datei.open(filename, ios::out);
 datei << Buffer << endl;
 datei.close();
}

int main()
{
 
 RamBufferedWrite test; 
 char d[100];
 for (int i = 0; i<99;i++)
 {
 char lastkey = getchar();
 if (lastkey == 10)
 {
 d[i+1]='\0';
 break;
 }
 d[i]=lastkey;
 d[i+1]='\0';
 }
 
 cout << "\nwie oft?";
 int times;
 cin >> times;
 while (times > 0)
 {
 test.WriteToBuffer(d);
 test.ShowBuffer();
 times--;
 }
 test.WriteToFile();
 test.WriteToFile("test.txt");
 system("pause");
 
 return 0;
}