Question

I was always curious.

Why does this work:

double Number = Convert.ToDouble(TextBox1.Text);

But this doesn’t:

double Number = (double)TextBox1.Text;

Answer 1

I think what you are asking is…

When I type this line of code into the IDE:

double Number = (double)TextBox1.Text;

Why can’t the compiler turn it into this implicitly:

double Number = Convert.ToDouble(TextBox1.Text);

The issue here is that you are using an explicit cast. What you are literally saying to the compiler is…

Even though I declared this chunk of memory to be X, I want you to treat it like a Y. The compiler is smart enough to know if it can be done or not. Since the chunk of memory you are trying to convert is a System.String, the compiler knows that there is no possible way to treat it as if it were a System.Double.

The static Convert methods are programatically parsing a value out and creating a brand new value in memory of the desired type, not simply using the same bytes in memory as though there were something else.