Question

why make things more complex? why do this:

txtNumerator.Text = 
     txtNumerator.Text == "" ? "0" : txtNumerator.Text;

instead of this:

if txtNumerator.Text="" {txtNumerator.Text="0";}

Answer 1

Suppose you wanted to pass either zero or txtNumerator.Text to a method M. How would you do that?

You could say:

string argument;
if (txtNumerator.Text == "")
{
    argument = "0";
}
else
{
    argument = txtNumerator.Text;
}
M(argument);

Or you could say

M(txtNumerator.Text == "" ? "0" : txtNumerator.Text);

The latter is shorter and easier to read.

The larger point here is that statements are useful for their side effects and expressions are useful for their values. If what you want to do is control which of two side effects happens, then use an “if” statement. If what you want to do is control which value gets chosen from two possibilities, then consider using a conditional expression.

UPDATE:

Jenny asks why not just do this?

if (txtNumerator.Text == "")
{
    M("0");
}
else
{
    M(txtNumerator.Text);
}

That’s fine if there’s just one condition to check. But what if there are, say, four? Now there are sixteen possibilities and writing the “if” statement for it gets messy to say the least:

if (text1.Text == "")
{
    if (text2.Text == "")
    {
        if (text3.Text == "")
        {
            if (text4.Text == "")
            {
                M("1", "2", "3", "4");
            }
            else
            {
                M("1", "2", "3", text4.Text);
            }
        }
        else
        {
            if (text4.Text == "")
            {
                M("1", "2", text3.Text, "4");
            }
            else
            {
                M("1", "2", text3.Text, text4.Text);
            }
        }
        ... about fifty more lines of this.

Instead, you can just say:

M(Text1.Text == "" ? "1" : Text1.Text,
  Text2.Text == "" ? "2" : Text2.Text,
  Text3.Text == "" ? "3" : Text3.Text,
  Text4.Text == "" ? "4" : Text4.Text);