How do I exit from a function?

Use the return keyword.

From MSDN:

The return statement terminates execution of the method in which it appears and returns control to the calling method. It can also return the value of the optional expression. If the method is of the type void, the return statement can be omitted.

So in your case, the usage would be:

private void button1_Click(object sender, EventArgs e) { if (textBox1.Text == "" || textBox2.Text == "" || textBox3.Text == "") { return; //exit this event } } 

return; // Prematurely return from the method (same keword works in VB, by the way) 

I'd suggest trying to avoid using return/exit if you don't have to. Some people will devoutly tell you to NEVER do it, but sometimes it just makes sense. However if you can structure you checks so that you don't have to enter into them, I think it makes it easier for people to follow your code later.

Use the return keyword.

return; //exit this event 

Yo can simply google for "exit sub in c#".

Also why would you check every text box if it is empty. You can place requiredfieldvalidator for these text boxes if this is an asp.net app and check if(Page.IsValid)

Or another solution is to get not of these conditions:

private void button1_Click(object sender, EventArgs e) { if (!(textBox1.Text == "" || textBox2.Text == "" || textBox3.Text == "")) { //do events } } 

And better use String.IsNullOrEmpty:

private void button1_Click(object sender, EventArgs e) { if (!(String.IsNullOrEmpty(textBox1.Text) || String.IsNullOrEmpty(textBox2.Text) || String.IsNullOrEmpty(textBox3.Text))) { //do events } } 

There are two ways to exit a method early (without quitting the program):

i) Use the return keyword.
ii) Throw an exception.

Exceptions should only be used for exceptional circumstances - when the method cannot continue and it cannot return a reasonable value that would make sense to the caller. Usually though you should just return when you are done.

If your method returns void then you can write return without a value:

return;