Reacting to Player Input - Learning C# by Programming Games - page 83

instruction is not true, and we use the else keyword for that:

if (mouse.LeftButton == ButtonState.Pressed)
{

double opposite = mouse.Y

−

barrelPosition.Y;

−

double adjacent = mouse.X barrelPosition.X;

angle = ( float )Math.Atan2(opposite, adjacent);

}
else
angle = 0f;

This instruction does exactly the same thing as the two if -instructions before, but we
only have to write down the condition once. Execute the Painter1b program and see
what it does. You will note that the angle of the cannon barrel is zero as soon as you
release the left mouse button.
The syntax of the if -instruction with an alternative is represented by the following
syntax diagram:

The reason that the body of an if -instruction can consist of multiple instructions
between braces is that an instruction can also be a block of instructions, which is
defined in the following syntax diagram:

6.4.2 A Number of Different Alternatives

When there are multiple categories of values, you can find out with if -instructions
which case we are dealing with. The second test is placed behind the else of the
first if -instruction, so that the second test is only executed when the first test failed.
A possible third test would be placed behind the else of the second if -instruction.
The following fragment determines within which age segment a player falls, so
that we can draw different player sprites: