Be aware that both Alt keys are not the same on some international keyboards!
Most PC Keyboards have an Alt key on either side of the Space Bar. In many countries, either of these keys may be used interchangeably.
However in some localities, especially those where accented characters are used, pressing the right-hand Alt Gr key has the same effect as pressing Alt + Ctrl together. It is used to generate a third character from certain keys.
For example, on the top row of a British keyboard, shifted 4 generates: $ (the Dollar Sign). If you hold down the Alt Gr key instead of the Shift key and press 4, it produces: € the Euro Currency Symbol instead.
Incidentally, in English braille, the Euro symbol is dot 4 plus e.