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Passing Parameters (C# Programming Guide)

In C#, arguments can be passed to parameters either by value or by reference. Passing by reference enables function members, methods, properties, indexers, operators, and constructors to change the value of the parameters and have that change persist in the calling environment. To pass a parameter by reference, use the ref or out keyword. For simplicity, only the ref keyword is used in the examples in this topic. For more information about the difference between ref and out, see ref (C# Reference), out (C# Reference), and Passing Arrays Using ref and out (C# Programming Guide).

The following example illustrates the difference between value and reference parameters.

class Program
    static void Main(string[] args)
        int arg;

        // Passing by value. 
        // The value of arg in Main is not changed.
        arg = 4;
        // Output: 4 

        // Passing by reference. 
        // The value of arg in Main is changed.
        arg = 4;
        squareRef(ref arg);
        // Output: 16 

    static void squareVal(int valParameter)
        valParameter *= valParameter;

    // Passing by reference 
    static void squareRef(ref int refParameter)
        refParameter *= refParameter;

For more information, see the following topics:

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

  • Parameters

  • 5.1.4 Value parameters

  • 5.1.5 Reference parameters

  • 5.1.6 Output parameters

  • 10.6.1 Method parameters