Question

int a=0;
int b=1;
int c=a,b;
int d=(a,b);

Answer 1

Outside of an initialization, the comma in a,b is the comma operator, and evaluates to b. The parentheses in the line involving d makes this such a case. So that line is really just equivalent to:

int d = b;

However, in the line involving c, this is not a use of the comma operator. Instead, it’s just a list of variable definitions, equivalent to:

int c = a;
int b;

(Which consequently will not compile, due to redefinition of b!)