Difference Between Ref and Out

Let’s clarify the difference between ref and out in C# — two ways to pass variables by reference

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📌 1. What They Do

Both ref and out allow a method to modify the caller’s variable directly, instead of working on a copy.

• ref → the variable must be initialized before passing.

• out → the variable does not need to be initialized, but must be assigned inside the method.

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📌 2. ref Example

void Increment(ref int x)
{
    x += 1;
}
 
int number = 5;
Increment(ref number);
Console.WriteLine(number); // Output: 6

Key Points:

• number must be initialized before passing.

• Changes inside the method affect the original variable.

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📌 3. out Example

void GetValues(out int a, out int b)
{
    a = 10; // Must assign inside method
    b = 20; // Must assign inside method
}
 
int x, y;            // Not initialized
GetValues(out x, out y);
Console.WriteLine($"{x}, {y}"); // Output: 10, 20

Key Points:

• x and y do not need initialization before passing.

• Method must assign a value to all out parameters before returning.

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📌 4. Differences Table

Feature	ref	out
Initialization required	Must be initialized before passing	No, can be uninitialized
Assignment inside method	Optional	Mandatory
Purpose	Pass value by reference, can read & modify	Pass value by reference, method must provide value
Common usage	Modify existing value	Return multiple values, output results

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📌 5. Combined Example

void Calculate(ref int num, out int square)
{
    num += 5;       // modifies original num
    square = num * num; // must assign square
}
 
int number = 3;
int result;
 
Calculate(ref number, out result);
 
Console.WriteLine(number); // 8
Console.WriteLine(result); // 64

• ref reads & modifies number

• out must be assigned result

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✅ Tip:

• Use ref when you want to modify an existing value.

• Use out when you want a method to return multiple values without initializing them first.