how to check if item is selected from a comboBox in C#

Use:

if(comboBox.SelectedIndex > -1) //somthing was selected

To get the selected item you do:

Item m = comboBox.Items[comboBox.SelectedIndex];

As Matthew correctly states, to get the selected item you could also do

Item m = comboBox.SelectedItem;

Here is the perfect coding which checks whether the Combo Box Item is Selected or not

if (string.IsNullOrEmpty(comboBox1.Text))
{
    MessageBox.Show("No Item is Selected"); 
}
else
{
    MessageBox.Show("Item Selected is:" + comboBox1.Text);
}

You seem to be using Windows Forms. Look at the SelectedIndex or SelectedItem properties.

if (this.combo1.SelectedItem == MY_OBJECT)
{
    // do stuff
}