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Decimals and rounding off

Posted on 2004-09-20
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Last Modified: 2010-08-05
I am trying to calculate the number of pages in a repeater based on the records returned and page size, but am having issue with decimals and rounding off. e.g.

iRecordCount = 18;
iPageSize = 10;

// Get total pages
decimal dPageRecords = Convert.ToDecimal(iRecordCount / iPageSize);
iTotalPages = Convert.ToInt32(System.Math.Round(dPageRecords));

Trace.Warn("dPageRecords=" + dPageRecords.ToString());
Trace.Warn("iTotalPages=" + iTotalPages);

Output I'm looking for is:
dPageRecords=1.8
iTotalPages=2

Whereas I keep fricking getting:
dPageRecords=1
iTotalPages=1

Any ideas thanks?
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Question by:jonnyboy69
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5 Comments
 
LVL 10

Accepted Solution

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eternal_21 earned 125 total points
ID: 12104622
 int iRecordCount = 18;
  int iPageSize = 10;

  double dPageRecords = (double)iRecordCount/(double)iPageSize;
  int iTotalPages = (int)Math.Ceiling(dPageRecords);

  Trace.Warn("dPageRecords=" + dPageRecords.ToString());
  Trace.Warn("iTotalPages=" + iTotalPages.ToString());

Will yeild the output you desire:

  dPageRecords=1.8
  iTotalPages=2
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LVL 10

Expert Comment

by:eternal_21
ID: 12104677
Another note: If you want one and only one decimal in your dPageRecords output, use this:

  Trace.Warn("dPageRecords=" + String.Format("{0:0.0}", dPageRecords));

Examples of output are:

  Value of dPageRecords -> Value of String.Format("{0:0.0}", dPageRecords)
  1.8 -> 1.8
  1.85447 -> 1.9
  1 -> 1.0

  So you will always have 1 decimal displayed.
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LVL 5

Expert Comment

by:tzxie2000
ID: 12105029
you can use
iTotalPages=(iRecordCount-(iRecordCount%iPageSize))/iPageSize+1
to get the pages
if you'd like to define pages as the page with full pagesize you can ommit +1 as
iTotalPages=(iRecordCount-(iRecordCount%iPageSize))/iPageSize
0
 
LVL 10

Expert Comment

by:eternal_21
ID: 12107478
jonnyboy69, I would suggest you use tzxie2000's solution for iTotalPages - it avoids any possibility of a rounding error.

  iTotalPages = iRecordCount/iPageSize + (iRecordCount%iPageSize==0 ? 0 : 1);
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LVL 1

Expert Comment

by:blueforce
ID: 12108218
The problem you've got is an order of operations problem.


This code is all well and good since an int can be implicitly cast "up" to a decimal:

decimal dPageRecords = Convert.ToDecimal(iRecordCount / iPageSize);
iTotalPages = Convert.ToInt32(System.Math.Round(dPageRecords));


However, look at the order of operations
Step 1.  iRecordCount / iPageSize  (both are ints so the answer will be an int - a rounded off int).
Step 2.  Convert the integer answer from Step 1 to a decimal
Step 3.  Assign the new decimal answer to dPageRecords.

It doesn't matter how big or small iRecordCount or iPageSize become - if you want to eventually hold a decimal, you'll have to explicitly cast to some floating type or use decimals to begin with.


The following will work since the casts happen before the division which results in the same datatype as the dividend and divisor:
decimal dPageRecords = Convert.ToDecimal( (decimal)iRecordCount / (decimal)iPageSize);  

Or you could just use decimals to begin with - the trade-off of a decimal datatype vs. the speed of explicitly casting an Int32 is about the same.

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