With the following stochastic-forecast model C = C * (1 + k * (rand - 0.5)) we are going to simulate an exchange rate.
Result
Implementation
// class variables
const double k = 0.02;
Random random = new Random();
chart1.Series[0].Points.Clear();
int days = (int) inputDays.Value;
double price = (double) inputPrice.Value;
chart1.Series[0].Points.AddXY(0, price);
for (int i = 1; i <= days; i++)
{
price = price * (1 + k * (random.NextDouble() - 0.5));
chart1.Series[0].Points.AddXY(i, price);
}