Converting a decimal to a fraction in C#

Question

I need to take a decimal like 4.625 and turn it into a fraction.  Does anyone have a class that will do it?  I found one but it gets stuck in a loop...  I copied the code here but if someone has a class that works, I'd appreciate it.  Thanks!

 

using System;
using System.Collections.Generic;
using System.Text;
public class UtilityNumberConversions
{
  public string dec2frac(double dblDecimal)
  {
    
    int intNumerator = 0;
    int intDenominator = 0;
    int intNegative = 0;
    // Declare integer variables 
    double dblFraction = 0;
    double dblAccuracy = 0;
    // Declare floating point variables as double precision.
    string txtDecimal = null;
    // need a string representation of the input value
    // in order to determine the required accuracy.

    // Find the accuracy needed for the output by checking the number of digits behind the decimal point
    //  of the input value.
    //
    //  dblAccuracy = 1 / 10 ^ (Len(CStr(dblDecimal - Fix(dblDecimal))) - 2)
    //
    //  While the formula above should work, there is a serious error in the way Excel handles
    //  decimal numbers and there's a huge rounding error issue. Subtracting the int() of
    //  12.1 from 12.1 produces 0.0999999999 or something similar. Obviously that won't
    //  work for our desired accuracy of the magnitude of the fractional part of the number
    //  so a slower more cumbersome method has to be used...

    dblAccuracy = 0.1;
    // Set the initial Accuracy level.
    txtDecimal = dblDecimal.ToString();
    // Get a string representation of the input number.

    // Check each character to see if it's a decimal point...
    for (int i = 0; i <= (txtDecimal.Length - 1); i++)
    {
      // if it is then we get the number of digits behind the decimal
      if (txtDecimal.Substring(i, 1) == ".")
      {
        dblAccuracy = 1 / Math.Pow(10, (txtDecimal.Length - i));
        //  assign the new accuracy level, and
        break; // TODO: might not be correct. Was : Exit For
        //  exit the for loop.
      }
    }

    intNumerator = 0;
    // Set the initial numerator value to 0.
    intDenominator = 1;
    // Set the initial denominator value to 1.
    intNegative = 1;
    // Set the negative value flag to positive.

    if (dblDecimal < 0)
    {
      intNegative = -1;
      // If the desired decimal value is negative,
      //  then set the negative value flag to
      //  negative.
    }

    dblFraction = 0;
    // Set the fraction value to be 0/1.

    // As long as we're still outside the
    while (Math.Abs(dblFraction - dblDecimal) < dblAccuracy)
    {
      //  desired accuracy, then...
      // If our fraction is too big,
      if (Math.Abs(dblFraction) > Math.Abs(dblDecimal))
      {
        intDenominator += 1;
        //  increase the denominator
        // Otherwise
      }
      else
      {
        intNumerator += intNegative;
        //  increase the numerator.
      }

      dblFraction = intNumerator / intDenominator;
      // Set the new value of the fraction.

    }

    return intNumerator.ToString() + "/" + intDenominator.ToString();
    // Display the numerator and denominator
  }
 

}

Answer 1

Here is one that I came up with a couple of years ago, try it out:

public static class FractionConverter
{
  public static string Convert(decimal value)
  {
    // get the whole value of the fraction
    decimal mWhole = Math.Truncate(value);

    // get the fractional value
    decimal mFraction = value - mWhole;

    // initialize a numerator and denomintar
    uint mNumerator = 0;
    uint mDenomenator = 1;

    // ensure that there is actual a fraction
    if (mFraction > 0m)
    {
      // convert the value to a string so that you can count the number of decimal places there are
      string strFraction = mFraction.ToString().Remove(0, 2);

      // store teh number of decimal places
      uint intFractLength = (uint)strFraction.Length;

      // set the numerator to have the proper amount of zeros
      mNumerator = (uint)Math.Pow(10, intFractLength);

      // parse the fraction value to an integer that equals [fraction value] * 10^[number of decimal places]
      uint.TryParse(strFraction, out mDenomenator);

      // get the greatest common divisor for both numbers
      uint gcd = GreatestCommonDivisor(mDenomenator, mNumerator);

      // divide the numerator and the denominator by the gratest common divisor
      mNumerator = mNumerator / gcd;
      mDenomenator = mDenomenator / gcd;
    }

    // create a string builder
    StringBuilder mBuilder = new StringBuilder();

    // add the whole number if it's greater than 0
    if (mWhole > 0m)
    {
      mBuilder.Append(mWhole);
    }

    // add the fraction if it's greater than 0m
    if (mFraction > 0m)
    {
      if (mBuilder.Length > 0)
      {
        mBuilder.Append(" ");
      }

      mBuilder.Append(mDenomenator);
      mBuilder.Append("/");
      mBuilder.Append(mNumerator);
    }

    return mBuilder.ToString();
  }

  public static decimal Convert(string value)
  {
    return 0m;
  }

  private static uint GreatestCommonDivisor(uint valA, uint valB)
  {
    // return 0 if both values are 0 (no GSD)
    if (valA == 0 &&
      valB == 0)
    {
      return 0;
    }
    // return value b if only a == 0
    else if (valA == 0 &&
          valB != 0)
    {
      return valB;
    }
    // return value a if only b == 0
    else if (valA != 0 && valB == 0)
    {
      return valA;
    }
    // actually find the GSD
    else
    {
      uint first = valA;
      uint second = valB;

      while (first != second)
      {
        if (first > second)
        {
          first = first - second;
        }
        else
        {
          second = second - first;
        }
      }

      return first;
    }

  }
}

---

public enum Answers { Everything = 0x2A }

Answer 2

http://www.vcskicks.com/decimal-to-fraction.php

 

 

public string ConvertToFraction(double dValue)
    {
      string frac = String.Empty;

      try
      {
        if (dValue > 2147483647 && dValue < 1.0 / 2147483647)
          frac = "not possible";
        if (dValue % 1 == 0)	// if whole number
          frac = dValue.ToString();
        else
        {
          double dTemp = dValue;
          int iMultiple = 1;
          string strTemp = dValue.ToString();
          int i = 0;
          while (strTemp[i] != '.')
            i++;
          int iDigitsAfterDecimal = strTemp.Length - i - 1;
          while (dTemp * 10 < 2147483647 && iMultiple * 10 < 2147483647 && iDigitsAfterDecimal > 0)
          {
            dTemp *= 10;
            iMultiple *= 10;
            iDigitsAfterDecimal--;
          }
          int temp1 = (int)Math.Round(dTemp);//numerator
          int temp2 = iMultiple;//denominator
          frac = ReduceFraction(temp1, temp2);
        }
        return frac;
      }
      catch (Exception)
      {
        return frac = "oops";
      }
    }
    public string ReduceFraction(int Numerator, int Denominator)
    {
      try
      {
        if (Numerator == 0)
        {
          Denominator = 1;
          return Numerator.ToString() + "/" + Denominator.ToString();
        }

        int iGCD = GCD(Numerator, Denominator);
        Numerator /= iGCD;
        Denominator /= iGCD;

        if (Denominator < 0)	// if -ve sign in denominator
        {
          //pass -ve sign to numerator
          Numerator *= -1;
          Denominator *= -1;
        }
        string temp1 = Numerator.ToString();
        string temp2 = Denominator.ToString();
        string frac = temp1 + "/" + temp2;
        return frac;

      } 
      catch (Exception exp)
      {
        return"Cannot reduce Fraction";
      }
    }
    private static int GCD(int iNo1, int iNo2)
    {
      // take absolute values
      if (iNo1 < 0) iNo1 = -iNo1;
      if (iNo2 < 0) iNo2 = -iNo2;

      do
      {
        if (iNo1 < iNo2)
        {
          int tmp = iNo1; // swap the two operands
          iNo1 = iNo2;
          iNo2 = tmp;
        }
        iNo1 = iNo1 % iNo2;
      } while (iNo1 != 0);
      return iNo2;
    }

http://forum.codecall.net/c-programming/8043-convert-any-double-fraction.html

---

mole on left eye

Answer 3

Thanks for this..  It appears to work just fine.  I appreciate your help.

Answer 4

Just as a matter of interest, you can write a greatest common divisor method more succinctly using recursion, like so:

static uint GreatestCommonDivisor(uint valA, uint valB)
{
    if (valB == 0)
        return valA;
    else
        return GreatestCommonDivisor(valB, valA % valB);
}

Answer 5

private string GetDisplayValue(string value)
        {
            try
            {
                decimal dc;

                if (!decimal.TryParse(value, out dc))
                    return value;

                if (dc == 0)
                    return "0";

                int a, b = 10000, c, d, e;
                decimal temp;

                temp = dc;

                temp = temp - (temp < 0 ? Math.Ceiling(temp) : Math.Floor(temp));

                a = (int) (temp*b);
                e = a;
                c = b;
                d = b;

                while (c != 0)
                {
                    d = c;
                    c = e%d;
                    e = d;
                }

                var sign = dc < 0 ? "-" : "";
                var whole = Math.Abs(temp < 0 ? Math.Ceiling(dc) : Math.Floor(dc)) == 0 ? string.Empty : Math.Abs(temp < 0 ? Math.Ceiling(dc) : Math.Floor(dc)) + " ";
                var fractionTop = Math.Abs(a)/Math.Abs(d) == 0 ? string.Empty : (Math.Abs(a)/Math.Abs(d)).ToString();
                var fractionBottom = Math.Abs(b)/Math.Abs(d) == 1 ? string.Empty : (Math.Abs(b)/Math.Abs(d)).ToString();
                var separator = fractionTop == string.Empty && fractionBottom == string.Empty ? string.Empty : "/";

                return string.Format("{0}{1}{2}{3}{4}", sign, whole, fractionTop, separator, fractionBottom).Trim();
            }
            catch
            {
                throw;
            }
       }

 

Answer 6

void Main()
{
	int w, n, d;
	RoundToMixedFraction(16.5675, 64, out w, out n, out d);
	Console.WriteLine("{0} {1}/{2}", w, n, d); // outputs: 16 9/16
}

void RoundToMixedFraction(double input, int accuracy, out int whole, out int numerator, out int denominator)
{
	double dblAccuracy = (double) accuracy;
	whole = (int)(Math.Truncate(input));
	var fraction = Math.Abs(input - whole);
	if(fraction == 0)
	{
		numerator = 0;
		denominator = 1;
		return;
	}
	var n = Enumerable.Range(0, accuracy+1).SkipWhile(e => (e/dblAccuracy) < fraction).First();
	var hi = n / dblAccuracy;
	var lo = (n-1) / dblAccuracy;
	if((fraction - lo) < (hi - fraction)) n--;
	if(n == accuracy)
	{
		whole++;
		numerator = 0;
		denominator = 1;
		return;
	}
	var gcd = GCD(n, accuracy);
	numerator = n / gcd;
	denominator = accuracy / gcd;
}

int GCD(int a, int b)
{
	if(b == 0) return a;
	else return GCD(b, a % b);
}