C#•2y ago

❔ ✅ Need help with methods and parameters

I'm stuck on the return methods, specifically how to use the ref and out keywords. Any sites or videos that discuss these topics in the console class?

9 Replies

Thinker•2y ago

If you're a beginner to the language then you really don't have to worry about ref and out or at least ref

AlexOP•2y ago

Well I guess that I'm not a beginner anymore. We covered those topics in my class and I just can't grasp how to use it

Thinker•2y ago

Have you ever used int.TryParse?

Buddy•2y ago

ref $refvsvalue

MODiX•2y ago

https://cdn.discordapp.com/attachments/364492811489509376/692833980650881084/pass-by-reference-vs-pass-by-value-animation.gif

cap5lut•2y ago

out -> the method u call will set it to a value, an earlier value would be overwritten, the variable can also be uninitialized.

public void Example1()
{
  int outValue;
  SetToFive(out outValue);
  Console.WriteLine(outValue); // will print 5
}

public void Example2()
{
  SetToFive(out int outValue);
  Console.WriteLine(outValue);
}

public void SetToFive(out int variable)
{
  variable = 5;
}

public void Example1()
{
  int outValue;
  SetToFive(out outValue);
  Console.WriteLine(outValue); // will print 5
}

public void Example2()
{
  SetToFive(out int outValue);
  Console.WriteLine(outValue);
}

public void SetToFive(out int variable)
{
  variable = 5;
}

Example1 and Example2 do exactly the same, the difference is simply that the variable declaration is "inlined", so u save one line of code to write, but thats it most common are the TryPase methods, as Thinker already mentioned. eg this to get an int number:

int someNumber;
while (true)
{
  Console.Write("Please write a number: ");
  string userInput = Console.ReadLine();
  if (int.TryParse(userInput, out someNumber)
  {
    break;
  }
  else
  {
    Console.WriteLine($"'{userInput}' is not a valid number, try again.");
  }
}

int someNumber;
while (true)
{
  Console.Write("Please write a number: ");
  string userInput = Console.ReadLine();
  if (int.TryParse(userInput, out someNumber)
  {
    break;
  }
  else
  {
    Console.WriteLine($"'{userInput}' is not a valid number, try again.");
  }
}

ref is similar to out, the main difference is that the called method doesnt have to set it to a value (its basically like a pointer in other languages)

public void Example()
{
  int someNumber = 5;
  MultiplyByTwo(ref someNumber);
  Console.WriteLine(someNumber); // will print 10
}

public void MultiplyByTwo(ref int number)
{
  number = number * 2;
}

public void Example()
{
  int someNumber = 5;
  MultiplyByTwo(ref someNumber);
  Console.WriteLine(someNumber); // will print 10
}

public void MultiplyByTwo(ref int number)
{
  number = number * 2;
}

to explain why these are needed goes into how parameters are passed. and there are 2 types of paramaters to think about, value types and reference types. value types are simple values like 5, 'a', -1.324 when calling a method, the value will be copied, and this copy is used in the method

public void Example()
{
  int someNumber = 5;
  MultiplyByTwo(someNumber);
  Console.WriteLine(someNumber); // this will print 5
}

public void MultiplyByTwo(int number)
{
  number = number * 2;
}

public void Example()
{
  int someNumber = 5;
  MultiplyByTwo(someNumber);
  Console.WriteLine(someNumber); // this will print 5
}

public void MultiplyByTwo(int number)
{
  number = number * 2;
}

it prints 5 for the reason, that when calling MultiplyByTwo(someNumber), the method has its own copy of the value. that copy will be modified in MultiplyByTwo(), but it does not affect someNumber at all in the previous examples using out/ref its a bit different. basically the memory of the variable is passed to the method, and the value at that address is modified this brings us to reference types:

public void Example()
{
  int[] someNumbers = new int[] { 1, 2, 3 };
  MultiplyByTwo1(someNumbers);
  MultiplyByTwo2(someNumbers);
}

public void MultiplyByTwo1(int[] numbers)
{
  for (int i = 0; i < numbers.Length; i++)
  {
    numbers[i] = numbers[i] * 2;
  }
}

public void MultiplyByTwo1(int[] numbers)
{
  var newArray = new int[numbers.Length];
  for (int i = 0; i < numbers.Length; i++)
  {
    newArray [i] = numbers[i] * 2;
  }
  numbers = newArray;
}

public void Example()
{
  int[] someNumbers = new int[] { 1, 2, 3 };
  MultiplyByTwo1(someNumbers);
  MultiplyByTwo2(someNumbers);
}

public void MultiplyByTwo1(int[] numbers)
{
  for (int i = 0; i < numbers.Length; i++)
  {
    numbers[i] = numbers[i] * 2;
  }
}

public void MultiplyByTwo1(int[] numbers)
{
  var newArray = new int[numbers.Length];
  for (int i = 0; i < numbers.Length; i++)
  {
    newArray [i] = numbers[i] * 2;
  }
  numbers = newArray;
}

references are pointing to some memory by default basically simply containing the memory address in both methods that reference is copied and passed to the respective method. in MultiplyByTwo1 that copy still points to the same memory and that memory is modified, so it really changes someNumbers in MultiplyByTwo2 a new memory block is created, the content written and then numbers (a reference to some memory) is replaced. but because this is just a copy of the reference, it doesnt affect someNumbers at all for that to happen u would have to use ref, so that a reference to the reference of the memory block is passed @Alex se Chipotle is ⤴️ understandable, or do u have questions?

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

AlexOP•2y ago

Thx. This helped

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

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❔ ✅ Need help with methods and parameters