How to find the top 10 highest and lowest numbers from a text file

[kevinzzz]

Hi guys,

I have a question, all help is truly appreciated. I have a list of numbers with decimal point saved in a text file (grade.txt) like this:

80.2
85.7
57.2
90.0
92.9
74.0
76.5
...
I would like to write a small program to display the top 10 highest and lowest grade points. I started learning C 3 weeks ago and right now I have no idea how to solve this problem. Someone please help.

[dealsoftheweek]

just sort the array and display first 3 and last 3 elements.

[Nepomuk]

Hi Kevinzzz and welcome to bytes.com!

There are several steps to solving that problem. First of all, you'll have to read the values into your program. Then you should sort them as suggested by dealsoftheweek. And finally you have to output the first and last 10 entries from the sorted array/list/whatever of saved values.

Personally I'd start in the middle: Create an array/list/whatever of values in the source code for testing (you would then call them "hardcoded") and try to sort them. There are many sorting algorithms available, Wikipedia lists a few of the most common. It's probably a good idea to start with a simple one, e.g. selection sort, and then possibly replacing it later on (if you so desire).

To check that the sorting worked you can output the first and last 10 entries. Especially if you're using an array that shouldn't be very difficult.

When you have that working, check on how to read values from text files. What you will get will probably be of the type char*, so find out how to turn them into float or double values. (Or int values if you like - depends on how accurate you need the algorithm to be.) As soon as you have those values, use the sorting and extracting algorithms you created before.

Each of these steps should be represented through (at least) one method/function. That way you can put them together relatively easily.

If you get stuck at any point you're welcome to ask here of course. If so, please show us what you have written so far and where the problem lies.

[donbock]

The following questions explore some details of exactly what you wish to accomplish.

1. Suppose the largest value occurs four times in the text file. Do you want that value to occur four times or only once in the output list?
2. Is the number of decimal digits in the input file a fixed value that you can hard-code into your program? If so then it will be easy to output values that look exactly like the input values. Otherwise you will either have to settle for outputting some values that look different than the input value (89.50 instead of 89.5) or you have to do something a little tricky to keep track of the number of decimal digits for each input value.
3. If the number of decimal digits can vary, then do you have any reason to distinguish between 75.4 and 75.40 (for example) when sorting or outputting the values?
4. Are you allowed to use standard library features to sort the values, or does your assignment forbid that?
5. Might the number of input values be so much larger than the number of output values (20) that sorting the entire input list in memory is inefficient?
6. What should happen if there are less than 20 values in the input list? (Highest and lowest output lists overlap)
7. What should happen if there are less than 10 values in the input list? (Can't fully populate the output lists)