Question

Why if do this:

Object bar;
Foo(bar);

in C# I get a

Use of unassigned local variable 'bar'

error?

How can I fix it?

Answer 1

How about assigning a value to the variable before you use it, as the error message states.

If you are passing the variable to a method you might want to take a look at using out keyword

The out keyword causes arguments to be passed by reference. This is
like the ref keyword, except that ref requires that the variable be
initialized before it is passed. To use an out parameter, both the
method definition and the calling method must explicitly use the out
keyword.

from the link you can see how to use the varaible if you wish to pass to a method and expect the variable to be initialised after that.

class OutExample
{
    static void Method(out int i)
    {
        i = 44;
    }
    static void Main()
    {
        int value;
        Method(out value);
        // value is now 44
    }
}