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operator (C# Reference)

Use the operator keyword to overload a built-in operator or to provide a user-defined conversion in a class or struct declaration.

The following is a very simplified class for fractional numbers. It overloads the + and * operators to perform fractional addition and multiplication, and also provides a conversion operator that converts a Fraction type to a double type.

class Fraction
{
    int num, den;
    public Fraction(int num, int den)
    {
        this.num = num;
        this.den = den;
    }

    // overload operator + 
    public static Fraction operator +(Fraction a, Fraction b)
    {
        return new Fraction(a.num * b.den + b.num * a.den,
           a.den * b.den);
    }

    // overload operator * 
    public static Fraction operator *(Fraction a, Fraction b)
    {
        return new Fraction(a.num * b.num, a.den * b.den);
    }

    // user-defined conversion from Fraction to double 
    public static implicit operator double(Fraction f)
    {
        return (double)f.num / f.den;
    }
}

class Test
{
    static void Main()
    {
        Fraction a = new Fraction(1, 2);
        Fraction b = new Fraction(3, 7);
        Fraction c = new Fraction(2, 3);
        Console.WriteLine((double)(a * b + c));
    }
}
/*
Output
0.880952380952381
*/

For more information, see the following sections in the C# Language Specification:

  • 7.2.2 Operator overloading

  • 7.2.3 Unary operator overload resolution

  • 7.2.4 Binary operator overload resolution

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