Sorting

I need to compute an arithmetic mean(average), median, and mode for up to 50 test scores.  The data are contained in a text file.  

To determine the median, I must first sort the array.  The median is the score in the middle of the range.  This can be determined by selecting the score at last/2 if last is odd.  The mode is the score that occurs the most often.  After building the frequency array, use it to determine which score occurred most often.  (Two scores can occur the same number of times)  I am working on a Unix operating system.