Conditional operators in C [duplicate]

Question

If the following code works

i=1;
i<10 ? printf("Hello") : printf("Bye");

then the assignment should also work.What is the reason which makes it to produce error?

i<10 ? foo=10 : foo=12;

Answer 1

What is the reason which makes it to produce error?

Operator precedence.

i<10 ? foo=10 : foo=12; is equivalent to (i<10 ? foo=10 : foo) = 12;

Use parentheses to fix your issue:

i<10 ? (foo=10) : (foo=12);

Answer 2

The reason is operator precedence. The following will work:

i<10 ? (foo=10) : (foo=12);

Your original expression gets parsed as

(i<10 ? foo=10 : foo)=12;

giving rise to the error (lvalue required as left operand of assignment).