Parameters

Parameters are optional variables that are used to pass data from outside in when calling a function. Their scope is inside the function. Parameters can be:

Required

Standard

What you'll be using most of the time:

int Add(int x, int y)
{
	return x + y;
}

int result = Add(2,3); //5

Input parameters

Marked with the in keyword, input parameters are read only and trying to change their value from within the function will result in a compiler error. Input parameter may have a default value.

void SomeOtherFunction(in int x)
{
	x = 5; //will show a compiler error because x cannot be changed
}

SomeOtherFunction(in 5);

Output parameters

Marked with the out keyword, output parameters must be assigned a value before exiting the function. Forgetting to do so will result in a compiler error. Only variables can be passed to out parameters.

void SomeOtherFunction(out int y)
{
	//will also show a compiler error because y must be given a value
}

int y;
SomeOtherFunction(out y);

Reference parameters

Marked with the ref keyword, these parameters are passed by reference. Only variables can be passed to ref parameters.

void YetAnotherFunction(ref int x)
{
	//do something
}

int x
YetAnotherFunction(ref x);

Optional

Optional parameters are given a default value when the function is defined. When the function is called, a value can be provided to them, but if one is not provided then the default value will be used. Optional parameters must be declared after required parameters

int Add(int x, int y = 5)
{
	return x + y;
}

When calling this function, you can provide a value for y or omit it:

Add(2,3);
Add(2); //5 will be used for y

Array parameters (params)

Marked with the params keywords, this function parameter is declared as an array, but used as if there were many separate parameters. Array parameters must be declared after optional parameters, and you can have only one.

int Sum(params int[] numbers)
{
	int sum = 0;
	foreach(int nr in numbers)
	{
		sum += nr;
	}
	return sum;
}

When calling this function, you can provide however many values, as if they were separate parameters:

Sum(1,2,3,4,5);