Calculating the mean of positive and negative numbers

Implement a program that reads 12 real numbers and calculates the mean of the positive and negative numbers. Afterwards, the result must be displayed to a maximum of 4 decimal places. Run the following test cases to test your program:

test case ID	inputs		expected outputs
		mean of positives	mean of negatives
1	1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12	6.5	0
2	-1, -2, -3, -4, -5, -6, -7, -8, -9, -10, -11, -12	0	-6.5
3	0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0	0	0
4	12.4, 21.005, -3.67, 4.43, 5.56, 4.2, 7, 8.3, -91.3, -1.0, 32.4, 12.1	11.9327	-31.99

Insist that the students test their programs by giving them example
test cases in a table. Series with only positive numbers, series
with only negative numbers, all zeros, and mix of positive/negative.