Fraction calculator problem

Hello would someone please help me with my program, I'm stuck all day with this thing. The program runs, but I think the problem is a logical error. The fraction 1/4 + 2 1/2 should be equal to 2 3/4 but the program's result is 2 3/8. Another thing is the expression 1/8 + 2 1/2 should be equals to 2 5/8. Please help me how to fix the codes. Thank you very much!

using System; class FractionDemo{ static void Main(string[] args) { Fraction firstfraction = new Fraction(); Fraction secondfraction = new Fraction(); firstfraction.Numerator = 1; firstfraction.Denominator = 4; secondfraction.Numerator = 1; secondfraction.Denominator = 8; secondfraction.WholeNumber = 2; Fraction add = new Fraction(); add = firstfraction + secondfraction; Console.Write("\n {0}/{1}", firstfraction.Numerator, firstfraction.Denominator); Console.WriteLine(" + {0}/{1} = {2}/{3}", secondfraction.Numerator, secondfraction.Denominator, add.Numerator, add.Denominator); Console.Write("\n {0}/{1}", firstfraction.Numerator, firstfraction.Denominator); Console.WriteLine(" + {0} {1}/{2} = {3} {4}/{5}", secondfraction.WholeNumber, secondfraction.Numerator,secondfraction.WholeNumber, add.WholeNumber, add.Numerator, add.Denominator); Console.Write("\n {0}/{1}", firstfraction.Numerator, secondfraction.Denominator); Console.WriteLine(" + {0} {1}/{2} = {3} {4}/{5}", secondfraction.WholeNumber, secondfraction.Numerator, secondfraction.WholeNumber, add.WholeNumber, add.Numerator, add.Denominator); Console.ReadLine(); } public class Fraction { private int wholenumber; private int numerator; private int denominator; public int WholeNumber { get { return wholenumber; } set { wholenumber = value; } } public int Numerator { get { return numerator; } set { numerator = value; } } public int Denominator { get { return denominator; } set { denominator = value; if (denominator > 0) { denominator = value; } else { denominator = 1; } } } public Fraction(int wholenumber, int numerator, int denominator) : this(numerator, denominator) { WholeNumber = wholenumber; } public Fraction(int numerator, int denominator) { WholeNumber = 0; Numerator = numerator; Denominator = denominator; } public Fraction() { WholeNumber = 0; Numerator = 0; Denominator = 1; } public int gcd() { int x = Numerator; int y = Denominator; int m; if (x > y) m = y; else m = x; for (int i = m; i >= 1; i--) { if (x % i == 0 && y % i == 0) { return i; } } return 1; } public void Reduce() { int gcdNum = gcd(); if (gcdNum != 0) { Numerator = Numerator / gcdNum; Denominator = Denominator / gcdNum; } if (Denominator < 0) { Denominator = Denominator * -1; Numerator = Numerator * -1; } convertFraction(); } public void convertFraction() { WholeNumber = Numerator / Denominator; Numerator = Numerator % Denominator; } public static Fraction operator +(Fraction firstfraction, Fraction secondfraction) { int firstNum = (firstfraction.WholeNumber * firstfraction.Denominator) + firstfraction.Numerator; int secondNum = (secondfraction.WholeNumber * secondfraction.Denominator) + secondfraction.Numerator; Fraction Result = new Fraction(); Result.Numerator = firstNum * secondfraction.Denominator + firstfraction.Denominator * secondNum; Result.Denominator = firstfraction.Denominator * secondfraction.Denominator; Result.Reduce(); return Result; } }}