Use of brackets in expression that include ternary operator

Question

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Error: lvalue required in this simple C code? (Ternary with assignment?)

In the following piece of code I got an error like "lvalue required as left operand of assignment". I am unable to understand why such an error is being reported. But when I am using parenthesis in the expression like (i>j)?(k=i):(k=j) it is not reporting an error. please explain.

int main() {
    int i = 2;
    int j = 9;
    int k;

    (i > j) ? k = i : k = j;
    printf("%d\n", k);

    return 0;
}

Answer 1

Without your extra ()s, I think the operator precedence is grouping it as

   ((i > j) ? k = i : k) = j;

Which obviously isn't what you want and does have lvalue issues.

Fix it with

  k = (i > j) ? i : j;

Answer 2

It's clear that this condition can be rewritten in a better way, but your problem is observed because of the precedence of = and ?: operators.

The assignment operator ?: has higher precedence than =, thus the expression

( i > j ) ? k = i : k = j;

Is equivalent to

(( i > j ) ? k = i : k) = j;

Which is not correct, because you cannot assign to an expression result.

In fact, this case is similar to (( i > j ) : i : j) = 10; which isn't correct either.

Answer 3

How about writing like this.

int main()
 {
   int i, j ,k;
   i = 2, j = 9;
   k = (i > j) ? i : j;

   printf("%d\n", k);
   return 0;
 }

Answer 4

Rather :

k = i > j ? i : j;