How to round a integer to the close hundred?

Question

I don\'t know it my nomenclature is correct! Anyway, these are the integer I have, for example :

76
121
9660

And I\'d like to round them to

Answer 1

Hi i write this extension this gets the next hundred for each number you pass

/// <summary>
    /// this extension gets the next hunfìdred for any number you whant
    /// </summary>
    /// <param name="i">numeber to rounded</param>
    /// <returns>the next hundred number</returns>
    /// <remarks>
    /// eg.:
    /// i =   21 gets 100
    /// i =  121 gets 200
    /// i =  200 gets 300
    /// i = 1211 gets 1300
    /// i = -108 gets -200
    /// </remarks>
    public static int RoundToNextHundred(this int i)
    {
        return i += (100 * Math.Sign(i) - i % 100);
        //use this line below if you want RoundHundred not NEXT
        //return i % 100 == byte.MinValue? i : i += (100 * Math.Sign(i) - i % 100);
    }

    //and for answer at title point use this algoritm
    var closeHundred = Math.Round(number / 100D)*100;

    //and here the extension method if you prefer

    /// <summary>
    /// this extension gets the close hundred for any number you whant
    /// </summary>
    /// <param name="number">number to be rounded</param>
    /// <returns>the close hundred number</returns>
    /// <remarks>
    /// eg.:
    /// number =   21 gets    0
    /// number =  149 gets  100
    /// number =  151 gets  200
    /// number = -149 gets -100
    /// number = -151 gets -200
    /// </remarks>
    public static int RoundCloseHundred(this int number)
    {
        return (int)Math.Round(number / 100D) * 100;
    }

Answer 2

I had a similar project internally where the business requirements were to search within the 100's range of a given number and find duplicate DB records. So if the user was using line 856 I would search 800 - 899. If the user was using 8567 I would search 8500 - 8599. Not an exact rounding by 100's, but thought I would include my unique approach as some of these basic coding questions are embedded within a larger business project. To test this I seeded a decimal list from 1 - 99999 and spit the results out into a file.

    /// <summary>
    /// This method accepts an inbound Line Number and returns the line range
    /// in the form of lowest to highest based on 100's
    /// Example would be 9122 returns 9100 - 9199
    /// It's used for generating some additional BOM Temp functionality.
    /// </summary>
    /// <param name="inboundNumber"></param>
    /// <returns></returns>
    public static ProjectLineRange CalculateLineRange(decimal inboundNumber)
    {
        var lineRange = new ProjectLineRange();
        var numberLength = inboundNumber.ToString(CultureInfo.InvariantCulture).Length;

        switch (numberLength)
        {
            case 0: //NULL?
                break;
            case 1: //Represents 1 - 9
                lineRange.LineBottom = 1;
                lineRange.LineTop = 99;
                break;
            case 2: //Represents 10 - 99
                lineRange.LineBottom = 1;
                lineRange.LineTop = 99;
                break;
            case 3: //Represents 100 - 999
                lineRange = CalculateHundredsRange((int)(inboundNumber / 100));
                break;
            case 4: //Represents 1000 - 9999
                lineRange = CalculateThousandsRange(
                    Convert.ToInt32(inboundNumber.ToString(CultureInfo.InvariantCulture).Substring(1, 1)),
                    Convert.ToInt32(inboundNumber.ToString(CultureInfo.InvariantCulture).Substring(0, 1)));
                break;
            case 5: //Represents 10000 - 99999
                lineRange = CalculateTenThousandsRange(
                    Convert.ToInt32(inboundNumber.ToString(CultureInfo.InvariantCulture).Substring(2, 1)),
                    Convert.ToInt32(inboundNumber.ToString(CultureInfo.InvariantCulture).Substring(1, 1)),
                    Convert.ToInt32(inboundNumber.ToString(CultureInfo.InvariantCulture).Substring(0, 1)));
                break;
        }

        return lineRange;
    }

public class ProjectLineRange
    {
       public decimal LineBottom { get; set; }
       public decimal LineTop { get; set; }
    }

    /// <summary>
    /// Helper method to return the range for the 100's place
    /// </summary>
    /// <param name="hundredsPlaceValue"></param>
    /// <returns></returns>
    public static ProjectLineRange CalculateHundredsRange(int hundredsPlaceValue)
    {
        var tempLineRange = new ProjectLineRange();
        tempLineRange.LineBottom = hundredsPlaceValue * 100;
        tempLineRange.LineTop = tempLineRange.LineBottom + 99;

        return tempLineRange;
    }

    /// <summary>
    /// Helper method to return the range for the 100's place when factoring a 1000's number
    /// </summary>
    /// <param name="hundredsPlaceValue"></param>
    /// <param name="thousandsPlaceValue"></param>
    /// <returns></returns>
    public static ProjectLineRange CalculateThousandsRange(int hundredsPlaceValue, int thousandsPlaceValue)
    {
        var tempLineRange = new ProjectLineRange();
        var tempThousands = thousandsPlaceValue * 1000;
        var hundredsRange = CalculateHundredsRange(hundredsPlaceValue);
        tempLineRange.LineBottom = tempThousands + hundredsRange.LineBottom;
        tempLineRange.LineTop = tempThousands + hundredsRange.LineTop;

        return tempLineRange;
    }

    /// <summary>
    /// Helper method to return the range for the 100's place when factoring a 10000's number
    /// </summary>
    /// <param name="hundredsPlaceValue"></param>
    /// <param name="thousandsPlaceValue"></param>
    /// <param name="tenThousandsPlaceValue"></param>
    /// <returns></returns>
    public static ProjectLineRange CalculateTenThousandsRange(int hundredsPlaceValue, int thousandsPlaceValue, int tenThousandsPlaceValue)
    {
        var tempLineRange = new ProjectLineRange();
        var tempThousands = thousandsPlaceValue * 1000;
        var tempTenThousands = tenThousandsPlaceValue * 10000;
        var hundredsRange = CalculateHundredsRange(hundredsPlaceValue);
        tempLineRange.LineBottom = tempTenThousands + tempThousands + hundredsRange.LineBottom;
        tempLineRange.LineTop = tempTenThousands + tempThousands + hundredsRange.LineTop;

        return tempLineRange;
    }

Answer 3

I wrote a simple extension method to generalize this kind of rounding a while ago:

public static class MathExtensions
{
    public static int Round(this int i, int nearest)
    {
        if (nearest <= 0 || nearest % 10 != 0)
            throw new ArgumentOutOfRangeException("nearest", "Must round to a positive multiple of 10");

        return (i + 5 * nearest / 10) / nearest * nearest;
    }
}

It leverages integer division to find the closest rounding.

Example use:

int example = 152;
Console.WriteLine(example.Round(100)); // round to the nearest 100
Console.WriteLine(example.Round(10)); // round to the nearest 10

And in your example:

Console.WriteLine(76.Round(100)); // 100
Console.WriteLine(121.Round(100)); // 100
Console.WriteLine(9660.Round(100)); // 9700