Does this code in C fall into the Undefined Behavior category?

Question

a is an array, foo is a function, and i is an int.

a[++i] = foo(a[i-1], a[i]);

Would

Answer 1

According to the C Standard (6.5.16 Assignment operators):

Semantics

3 ...The evaluations of the operands are unsequenced.

Thus this statement

a[++i] = foo(a[i-1], a[i]);

results in undefined behavior.