Write a program to calculate the geometric mean of numbers entered by a user. The program should prompt the user to enter numbers and continue to accept the numbers until the user enters 999.

Note: Do not include 999 when calculating the average.

The geometric mean of a set of numbers (x₁, x₂, ... x_n) is given by:

(X1 * X2 ...Xn)^ 1/n

For example, the geometric mean of 3, 5, 7 and 9:

(3*5*7*9)^ 1/4 = 5.5444

The flow of the program should be as follows:

1. Prompt the user to enter a number
2. User enters a number
3. Process the number
4. Program continues to prompt user to enter numbers (repeat steps 1-3) until user enters 999
5. Program displays the message 'The geometric mean is ' and then prints the mean of all the entered numbers (excluding 999) to the screen