Difference Between ref and out keywords in C#

Both ref and out are used to pass arguments by reference in C#.

That means the method can modify the original variable value.

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1. ref Keyword

• Variable must be initialized before passing

• Used when method reads and modifies the value

• Memory must already contain a value

Example

void AddTen(ref int number)
{
    number = number + 10;
}

int x = 5;
AddTen(ref x);
// x becomes 15

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2. out Keyword

• Variable does NOT need initialization before passing

• Method must assign a value before returning

• Used mainly for returning multiple values

Example

void GetNumber(out int number)
{
    number = 20;
}

int x;
GetNumber(out x);
// x becomes 20

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Key Differences (List Format)

1. Initialization

   • ref → Must initialize before passing

   • out → No need to initialize before passing

2. Value Assignment Inside Method

   • ref → Optional to assign

   • out → Mandatory to assign

3. Usage Purpose

   • ref → Modify existing value

   • out → Return value from method

4. Memory

   • Both pass variable reference (same memory location)

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Simple Rule to Remember

• If variable already has value → use ref

• If method will create and return value → use out