Why different behavior in two cases 1st. int i = 1,2,3; and 2nd. int i; i = 1,2,3; [duplicate]

Answer 1

1. In the first case the comma separates declaration and initialisation of several variables of the same type:

   int i = 1, j = 2, k = 3;
   

   You can add parentheses to tell the compiler it's an expression.

   int i = (1, 2, 3);
   

   If you combine them, it's easier to see why the comma is ambiguous without parentheses:

   int i = (1, 2, 3), j = 4, k = 5;
   

2. In the second case the comma separates 3 expressions.

   (i = 1), 2, 3