Retrieving Mathematical formulae and manipulating them with C++?

[luckiejacky]

#define formula_( operand0, operator0, operand1 ) printf_s("%d %s %d", ##operand0, ##operator0, ##operand1 )
  
int red = 1;
int green = 2;
int blue = 3;

int v = formula_(red, "+", blue);

How come the answer is five? What is the best way to store mathematical formulae? This is basically run-time thing, I can't build them in.
thanks
Jack