Code similar to the one below will do it for you
.....
public class Form1()
{
private bool incremented;
private int numToIncrement;
........
public Form1()
{
numToIncrement=0;
incremented = false;
}
private void button1_Click(.......)
{
numToIncrement =
if(!incremented)
{
numToIncrement++;
}
else
{
}
incremented = true;
}
........
}