Please explain the output of the following program.

Question

#include<stdio.h>

 

int main(void)

{

    int a = 1, 2, 3;

    printf("%d", a);

    return 0;

}

Answer 1

it is not syntactically correct, it will give comiler error...

if you would have written

int a=(1,2,3);

then a =3 will be initialized because comma operator are left asscociative, finally 3 will be lvalue which will be supllied to rvalue(a)..

Answer 2

It will give compilation error.

If you write it as

int a;

a=1,2,3

then it will work fine.

Why?

Comma operator has least precedence ( = has higher precedence than, operator)  so it will be like

(a=1), 2, 3;
Output will be 1 in this case. But for the mentioned question it gives Compilation Error.

Comments

no it will give compiler,

int (a=1),2,3;

the code is declaring 2 and 3 as an int(which is invalid) since they are constant(3,4), they cant be declared...

(a=1),2,3; is written anyplace other than declaraion than it was right..

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Updated answer @joshi