c++ scanf always expects double and not float
float max, zz, rate, time, percent;
printf("Please enter the size (in GB): ");
scanf_s("%f", &max);
printf("\nPlease enter how much you have downloaded already (in GB): ");
scanf_s("%f", &zz);
printf("\nPlease enter the downloadrate (in kB/s): ");
scanf_s("%f", &rate);