Macro with do–while and external counter: how many times does it print? #include<stdio.h> #define FUN(arg) do { if (arg) printf("CuriousTab..."); } while (--i) int main() { int i = 2; FUN(i < 3); return 0; }

Introduction / Context:
This question highlights macro expansion, the common do–while(0) pattern (here slightly altered), and how a macro can legally reference and change a variable in the surrounding scope. It also examines short-circuit evaluations inside the loop body.

Given Data / Assumptions:

• i is defined in main and visible to the macro expansion.
• The macro expands to a do { ... } while(--i) loop.
• The printf has no format specifiers; any extra argument would be ignored if present.

Concept / Approach:
Start with i = 2. The do executes once unconditionally, the if (i < 3) is true, so it prints once. Then the loop condition --i decrements i to 1, which is nonzero, so the loop repeats. On the second pass, the condition is still true, it prints again, and --i turns 1 to 0, terminating the loop. Total prints = 2.

Step-by-Step Solution:

Verification / Alternative check:
Add printf(" i=%d\n", i); after the printf to trace the countdown 2 → 1 → 0.

Why Other Options Are Wrong:

Common Pitfalls:
Forgetting that the macro reuses the caller’s i; assuming the do–while always uses 0 in its condition.

Final Answer:
CuriousTab... CuriousTab....