In C what exactly happens if i use () to initialize a double dimension array instead of the {}?

Question

When I initialize an array a[][]:

int a[2][5]={(8,9,7,67,11),(7,8,9,199,89)};

and then display the array elements.

Why do I get:

11 89 0 0 0 
0 0 0 0 0

What happens if you use curly braces instead of the first brackets here?

Answer 1

(8,9,7,67,11)

is an expression using the comma operator that evaluates to 11. The same holds for the other initialiser. So you only initialise the first two elements explicitly, all others are then initialised to 0. Your compiler should warn about a missing level of braces in the initialiser.

If you use curly braces, you initialise the two component arrays of a, as is probably intended.

Answer 2

 int a[2][5]={(8,9,7,67,11),(7,8,9,199,89)};

is equivalent to (at block scope):

 int a[2][5]={11, 89};

, is the C comma operator. It evaluates its operands from left to right and yields the value of the right operand.

At file scope array initializers must be constant and as the , expression is never a constant expression, you array declaration is invalid.