int numeros = 0;
int media = 0;
int n;
while (cin >> n and n != -1) {
   if (n >= 1 and n <= 100) {
     ++numeros;
     media += n;
   }
}

cout << "cantidad de numeros entre 1 y 100: " << numeros << endl;
cout << "media: " << media/numeros << endl;