Editing Parameter (computer programming) (section)

===Use===
The primary use of output parameters is to return multiple values from a function, while the use of input/output parameters is to modify state using parameter passing (rather than by shared environment, as in global variables). An important use of returning multiple values is to solve the [[semipredicate problem]] of returning both a value and an error status – see [[Semipredicate problem#Multivalued return|Semipredicate problem: Multivalued return]].

For example, to return two variables from a function in C, one may write:
<syntaxhighlight lang="c">
int width
int height;

F(x, &width, &height);
</syntaxhighlight>
where <code>x</code> is an input parameter and <code>width</code> and <code>height</code> are output parameters.

A common use case in C and related languages is for [[exception handling]], where a function places the return value in an output variable, and returns a Boolean corresponding to whether the function succeeded or not. An archetypal example is the <code>TryParse</code> method in .NET, especially C#, which parses a string into an integer, returning <code>true</code> on success and <code>false</code> on failure. This has the following signature:<ref>[http://msdn.microsoft.com/en-us/library/f02979c7.aspx Int32.TryParse Method (String, Int32)]</ref>
<syntaxhighlight lang="csharp">
public static bool TryParse(string s, out int result)
</syntaxhighlight>
and may be used as follows:
<syntaxhighlight lang="csharp">
int result;
if (!Int32.TryParse(s, result)) {
    // exception handling
}
</syntaxhighlight>
Similar considerations apply to returning a value of one of several possible types, where the return value can specify the type and then value is stored in one of several output variables.