Less Than

The < (less than) operator is a binary relational operator that evaluates whether its left-hand operand is strictly less than its right-hand operand, returning a bool result.

int leftOperand = 5;
int rightOperand = 10;
bool result = leftOperand < rightOperand; // Evaluates to true

Type Support and Numeric Promotion The operator is natively defined for all built-in integral (sbyte, byte, short, ushort, int, uint, long, ulong, nint, nuint) and floating-point (float, double, decimal) numeric types. When operands are of mixed numeric types, C# applies implicit numeric promotion to convert them to a common type before evaluation.

The operator is also natively supported for:

• char: Evaluates the underlying 16-bit Unicode integer values.
• enum: Evaluates the underlying integral values of the enumeration members.
• Pointer types (T*): Evaluates the memory addresses held by the pointers, requiring an unsafe context.

Floating-Point Evaluation Rules When evaluating float or double types, the operator adheres to IEEE 754 standards. If either the left or right operand evaluates to Not-a-Number (NaN), the < operator strictly returns false.

double x = double.NaN;
double y = 5.0;
bool isLess = x < y; // Evaluates to false

Lifted Operators for Nullable Types For nullable value types (T?), C# provides lifted operators. The lifted < operator safely evaluates the operands by checking their HasValue properties rather than blindly unwrapping them. If either or both operands evaluate to null (meaning HasValue is false), the result of the < operation is always false.

int? a = null;
int? b = 10;
bool isLess = a < b; // Evaluates to false

Operator Overloading User-defined types (class, struct, or record) can overload the < operator to define custom comparison logic. C# enforces a strict pairing rule for relational operators: if a type overloads the < operator, it must also explicitly overload the > (greater than) operator.

public readonly struct Temperature
{
    public double Value { get; }

    public Temperature(double value) => Value = value;

    public static bool operator <(Temperature left, Temperature right)
    {
        return left.Value < right.Value;
    }

    public static bool operator >(Temperature left, Temperature right)
    {
        return left.Value > right.Value;
    }
}

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