Why am I getting these out parameter errors in C#?

Question

I am new to C#. I\'ve tried this with out parameter in C#

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
class Firs         


        

Answer 1

As of C# 7.0 the ability to declare a variable right at the point where it is passed as an out argument was introduced.

Before:

public void PrintCoordinates(Point p)
{
    int x, y; // have to "predeclare"
    p.GetCoordinates(out x, out y);
    WriteLine($"({x}, {y})");
}

C# 7.0

public void PrintCoordinates(Point p)
{
    p.GetCoordinates(out int x, out int y);
    WriteLine($"({x}, {y})");
}

You can even use var key word:

p.GetCoordinates(out var x, out var y);

Be carefull with the scope of out parameter. For example, in the following code, "i" is only used within if-statement:

public void PrintStars(string s)
{
    if (int.TryParse(s, out var i)) { WriteLine(new string('*', i)); }
    else { WriteLine("Cloudy - no stars tonight!"); }
}

Further information can be found here. This link is not only about out parameter, but all the new features introduced in c# 7.0