Input and Output parameters

15y1.2kAzure

Hi,

Im aware parameters within a parenthesis are by default input parameters.

And I know that by placing out in front of the type of each parameter delcares it as an output, but Im not understanding exactly how and why these are used surely the return would do this job?

Regards,

12 Replies

Know the answer? Post it — somebody with the same question will find it here.

Guest User15y ago
Accepted answer
If you only need to have one value returned from a method, then there's not much point to using an output parameter -- as you said, the return statement would do the job.

However there may be occasions where you would need to declare a method as return-type void, in which case an output parameter would be the only way to get a return value.
15y ago
Thanks,

John's "Accepted Answer" restored.
Vulpes15y ago
That was a case where I was altering someone else's code. If I'd been writing it myself I'd have done:

public double GetInvestment(string sPrompt){ ... }

Also a couple of further points about 'out' parameters:-

1. Unlike 'ref' parameters, it's not necessary to initialize the variable. So, in Raja's code, he could have done:

double dvalue;

2. The compiler guarantees that the 'out' parameter will have been assigned a value by the time the method returns.

P.S. You've taken away John's 'Accepted Answer' ! It's a good idea to ask a new question on a new thread so other posters such as Raja can be given credit for answering it correctly.
15y ago
Thanks Raja! The order in which I wrote the method parameters was a typo.
Raja Krishnamurthy15y ago
public void GetInvestment(out double dvalue, string sPrompt)

This method is accepting\passing in 1 input parameter "double dvalue" and 1 output parameter "string sPrompt".

I think you got this wrong. He is passing two parameters of which sPrompt is the input while he expects the output of the method GetInvestment to be populated into dvalue which is the output parameter hence the keyword "out" is prefixed to the parameter.

He would now invoke the method something like this:

double dvalue; //Good point on the assignment Vulpes corrected :-)
string sPrompt = "some input value";
GetInvestment(out dvalue,sPrompt);
Console.WriteLine("Investment is : {0}", dvalue); //displaying the calculated investment

Also to get a better understanding of methods and parameters check out the recommended articles section.

HTH.
15y ago
Hi Vulpes,

Given the below line of code I sourced from another articles answer of yours...

public void GetInvestment(out double dvalue, string sPrompt)

This method is accepting\passing in 1 input parameter "double dvalue" and 1 output parameter "string sPrompt".

Am I write in saying that the point of giving this method the 2 parameters within the parentheses rather than the body of the method is so when the method is called the user\caller must insert the corresponding arguments of which then the triggering to initialize the components is defined and referenced in the body...
Sam Hobbs15y ago
The return value is often used for an error indication. When the data is returned from the function then there is either not a way to return an error or the error must be returned in a parameter. Returning the data as a parameter is more logical than returning an error code as a parameter. In situations that an error is not relevant, it is logical to return the data as the return value.
Guest User15y ago
Thanks Vulpes!
Vulpes15y ago
Give it to John, I've had a couple already today :)
15y ago
Thanks John & Vulpes both great answers! : )

Im torn as to who to give the Accepted answer to?
Vulpes15y ago
A good example of an 'out' parameter enabling you to return multiple values is the Int32.TryParse() method:

int num;
string s = "42";
bool isValid = Int32.TryParse(s, out num); // return type of bool
if (isValid)
{
Console.WriteLine("The number is {0}", num); // 42
}
else
{
Console.WriteLine("The number was invalid but has been given a default value of {0}", num); // default is zero
}
Vulpes15y ago
Output parameters can be used if you want to return more than one value from a method.

In C# 4.0 you can also use a Tuple for this purpose.