C++ Constructor initialization list with array

Question

What am I doing wrong here? The compiler tells me it is a syntax error.

class Color {
private:
 float rgba[4];
public:
 Color(float red, float green, float blue, float alpha=1.0):
 this->rgba[0] (red * alpha),
 this->rgba[1] (green*alpha)
 this->rgba[2] (blue*alpha)
 {
 }
};

• Martin Beckett: I know this is probably just a homework exercise. But check if your graphics lib really wants RGBA pre-multiplied by A
• happy_sisyphus: Is it a bad idea to multiply by A? Could you please tell me more about it?
• Martin Beckett: The reason for the "A" is to change the all the colors at once, to handle overlaying images etc. Normally the graphics hardware would do the multiplication at display time.
• M.M: this->rgba[0] is an error. The only thing that can appear after : is a member identifier, i.e. rgba is the only option for this class

Answer 1

It should be

Color(float red, float green, float blue, float alpha=1.0):
 rgba{red * alpha, green*alpha, blue*alpha, 0}
 {
 }

• David Hammen: This assumes a C++11 compliant compiler. Some people still aren't using C++11.
• M.M: Some people haven't discovered computers yet so we should print this answer out and do a leaflet drop

Answer 2

You can use the asigment operator instead of parentetheses:

this->rgba[0](red * alpha) // wrong
this->rgba[1] = red * alpha // ok