The C# operators fall into four main categories: arithmetic, comparison, logical, and bitwise. The following sections explain these categories and the operators they contain. The end of this appendix describes operator precedence and special operators, as well as operator overloading.

Arithmetic Operators

The following table lists the arithmetic operators provided by C#.

Comparison Operators

The following table lists the comparison operators provided by C#.

Logical Operators

The following table summarizes the C# logical operators.

Bitwise Operators

Bitwise operators work much as logical operators do, except that they compare values 1 bit at a time. C# provides bitwise versions of the &, |, and ^ operators. It also provides ~, the bitwise negation operator.

Assignment Operators

Many operators have assignment versions. For example, the following code adds 10 to the value x and saves the result in variable x.

x += 10;

The complete list of assignment operators is: =, +=, -=, *=, /=, %=, &=, |=, ^=, <<=, and >>=.

Conditional and Null-coalescing Operators

The conditional operator ?: (sometimes called the ternary operator) takes three operands. If the first operand is true, it returns the second operand. Otherwise it returns the third operand.

The null-coalescing operator ?? takes two operands. It returns its left operand if its value is not null. If the left operand is null, it returns its right operand.

Operator Precedence

The following table lists the operators in order of precedence. When evaluating an expression, the program evaluates an operator before it evaluates those in a lower section of the list.

When operators are in the same section in the table, or if an expression contains more than one instance of the same operator, the program evaluates them in left-to-right order.

Use parentheses to change the order of evaluation and to make expressions easier to read.

DateTime and TimeSpan Operators

The DateTime and TimeSpan data types are related through their operators. The following list shows the relationships between these two data types.

• DateTime − DateTime = TimeSpan
• DateTime + TimeSpan = DateTime
• TimeSpan + TimeSpan = TimeSpan
• TimeSpan − TimeSpan = TimeSpan

The following table lists examples demonstrating convenient methods provided by the DateTime data type.

Operator Overloading

To overload an operator, create a static method that returns the appropriate data type. Instead of giving the method a name, use the keyword operator followed by the operator symbol you want to overload. Next, define the parameters that the operator takes. Finally, write the code that the operator should execute.

For example, the following code defines a + operator for a simple Complex class.

public static Complex operator +(Complex operand1, Complex operand2)
{
    return new Complex()
    {
        Re = operand1.Re + operand2.Re,
        Im = operand1.Im + operand2.Im
    };
}

Unary operators that you can overload include: +, -, !, ~, ++, --, true, and false.

Binary operators that you can overload include: +, -, *, /, %, &, |, ^, <<, and >>. If you overload true, false 7, and |, the && and || operators are automatically overloaded for you.

Note that the second operand for the shift operators << and >> must be an int.

The assignment operators are automatically overloaded if you overload the corresponding operator. For example, if you overload *, then C# overloads *= for you.

See Chapter 5, “Operators,” for more information about overloading comparison, logical, and type conversion operators.