Calculating daily averages

Hi, I am not an expert in excel and I am having trouble calculating averages using date constraints. In the worksheet I have a column that contains the date and time and another column that contains the temperature. The amount of measurments per day vary from 24 or less. I need to calculate the average daily temperature for each day of the year for 5 years.

Example
Column A Column B Column C
5/13/10 23:44 30
5/13/10 22:44 27
5/13/10 21:44 29
5/13/10 20:44 30
.
.
.
.
1/8/10 5:44 10


Any help would be greatly appreciated, Thanks!

Assuming your data goes to row 501 and in Column E beginning with E1, you have the dates of interest. In F1

=SUMIF($A$2:$A$501,E1,$C$2:$C$501)/COUNTIF($A$2:$A$501,E1)

Does that work for you?