Difference between “int i=1,2,3” and “int i=(1,2,3)” - variable declaration with comma operator [duplicate]

Answer 1

Statement 1 Result : Compile error.

'=' operator has higher precedence than ',' operator. comma act as a separator here. the compiler creates an integer variable 'i' and initializes it with '1'. The compiler fails to create integer variable '2' as '2' is not a valid indentifer.

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Statement 2 Result: i=3

'()' operator has higher precedence than '='. So , firstly, bracket operator is evaluated. '()' operator is operated from left to right. but it is always the result of last that gets assigned.

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Statement 3: Result: i=1

'=' operator has higher precedence than ',' operator. so 'i' gets initialized by '1'. '2' and '3' are just constant expression. so have no effect .

Answer 2

It is the comma operator

i = a, b, c;            // stores a into i      ... a=5, b=2, c=3, i=5


i = (a, b, c);          // stores c into i      ... a=5, b=2, c=3, i=3

the differing behavior between the first and second lines is due to the comma operator having lower precedence than assignment.