Last post May 25, 2017 11:21 AM by HamtekBusinessSoftware
May 17, 2017 01:45 PM|HamtekBusinessSoftware|LINK
Hi guys. I have this simple function in Delphi
function Round45 (Value : Real; RPower : Integer) : Real;
Result := Trunc (Value * Power (10, RPower) + 0.5)/Power (10, RPower);
It's purpose was to provide a result in the range from 0 to 100.
I am attempting to convert that function to c#
I have tried using Math.Round but that produces a double - I require an integer from 0 to 100.
Any help would be appreciated.
May 17, 2017 04:09 PM|HamtekBusinessSoftware|LINK
Oh, it seems I can just use
int result = Convert.ToInt32(correctAnswers * 100) / NoOfQuestions);
So, for example, if I have 20 questions taken and the user obtains 9 correct answers, the code produces 45 which is just what I required.
May 18, 2017 09:38 AM|HamtekBusinessSoftware|LINK
My previous works well for 2 and 20 questions, but fails with say 6 questions correct out of 13 questions.
This new code corrects that error
int result = Convert.ToInt32(Math.Round(((correctCount * 100f / questionCount) * Math.Pow(10, 10) + 0.5) / Math.Pow(10, 10)));
Note the 100f which was all that was missing form my first attempt and removes the need for a double cast.
Hope this info helps someone.
May 22, 2017 04:46 AM|PaulTheSmith|LINK
Have you worked through, on paper, what your code is doing?
If correctCount = 6 and questionCount = 13 then this is what happens (what is the type of these variables???)
First multiply correctCount by 100 to get
Now divide by 13 to get, approximately
Now you multiply by Mth.Pow(10,10) which is a huge number to get
Now you add 0.5 to get
now divide by the same huge number to get back to the number you started with (except for an amount less than the width of an electron)
and then you round it to get
and then you convert to Int32 to get
Wow! That was a long journey.
If the input variables are integers then
int result = correctCount*100/questionCount
will give the same result.
If they are not integers then what are they?
May 22, 2017 09:28 AM|HamtekBusinessSoftware|LINK
The inputs are integers, so where as:
using correctCount = 6 and questionCount = 13
int result = (6 * 100) /13 gives a result of 46 which is correct when rounding 46.15
but, if you use correctCount = 7 and questionCount = 13
int rrsult = (7 * 100)/13 gives a result of 53 however rounding 53.84 shows the result should be 54.
My code gives the correct answer of 54.
So I don't think I can use simple integer maths.
If you have a simple formula the gives 5/4 rounding of integers, please let me know.
May 24, 2017 10:32 PM|PaulTheSmith|LINK
var result = Math.Round(correctCount*100f/questionCount);
May 25, 2017 06:39 AM|HamtekBusinessSoftware|LINK
Thanks Paul. That seems to work. I shall have to fully test it.
Thanks for the help and your time.
May 25, 2017 11:04 AM|HamtekBusinessSoftware|LINK
Hi Paul. I have tested your equation and mine in a double for loop going from a questionCount of 10 to 30 in the outer loop and a correctCount of 1 to the current questionCount
in the inner loop. This let me test all the permutations.
Your code worked well in almost all loop iterations. the only discrepancy was with the following values:
1) correctCount 2 and questionCount 16 gave a fraction 2/16 = 0.125 - my equation gave this as 13% whereas your equation gave it as 12%
2) correctCount 10 and QuestionCount 16 gave a fraction 10/16 = 0.625 - my equation gave this as 63% whereas your equation gave it 62%
3) correctCount 3 and questionCount 24 gave a fraction 3/24 = 0.125 - my equation gave this as 13% whereas your equation gave it 12%
4) correctCount 15 and questionCount 24 gave a fraction 15/24 = 0.625 - my equation gave this as 63% whereas your equation gave 62%
You can see two of the problem values are 0.125 and 0.625.
Anything that can be done to correct this rounding error?
May 25, 2017 11:21 AM|HamtekBusinessSoftware|LINK
Ahh, all it needed was the MidpointRounding parameter
var val1 = Math.Round(correctCount * 100f / questionCount, MidpointRounding.AwayFromZero);