Understand difference between C# ref and out keywords

Aspect	ref	out
Initialization Required	No, must be initialized before passed	No, must be assigned inside the method
Value Before Passing	Yes, variable must have a value before passing	No, variable can be uninitialized
Usage Inside Method	Can use the variable's initial value	Must assign a value before returning
Return Value	Can return any value including the initial value	Must assign a value before returning
Use Case	Used when you want to pass a variable by reference and also allow the method to read or modify the variable	Used when you want the method to assign a value to the variable and return it

• ref: initialization required, Bi-directional.
• out: initialization not required, Unidirectional(from method to caller)

Pass by Value Addition

int a = 5;
int b = 10;

int sum = 0;
int product = 0;

static void Addition(int a, int b, int sum, int product)
{
    sum = a + b;
    product = a * b;
}

Addition(a, b, sum, product);

Console.WriteLine(sum + " " + product);

/**
 * Output: 0 0
 * 
 * It does not work because the value of sum and product are changed inside method only.
 The values of sum and product outside the addition does not change.
 */

Pass by Reference using 'ref' Keyword

int a = 5;
int b = 10;

int sum = 0;
int product = 0;

static void Addition(int a, int b, ref int sum, ref int product)
{
    sum = a + b;
    product = a * b;
}

Addition(a, b, ref sum, ref product);

Console.WriteLine(sum + " " + product);

/**
 * Outptut: 15 50
 */

Pass by Output using 'out' Keyword

int a = 5;
int b = 10;

int sum = 0;
int product = 0;

static void Addition(int a, int b, out int sum, out int product)
{
    sum = a + b;
    product = a * b;
}

Addition(a, b, out sum, out product);

Console.WriteLine(sum + " " + product);

/**
 * Output: 15 50
 */