GATE CS 2019 Q27 — Programming in C

The function r() uses a static variable num initialized to $7$. The post-decrement operator num-- returns the current value of num and then decrements it by $1$.

Let's trace the execution of the for loop step-by-step:

1. Initialization: r() is called.
   • Returns $7$ (ignored).
   • num becomes $6$.
2. First Iteration:
   • Condition: r() is evaluated. Returns $6$ (non-zero, so true). num becomes $5$.
   • Body: printf("%d", r()) is executed. r() returns $5$ and num becomes $4$. This prints 5.
   • Increment: r() is called. Returns $4$. num becomes $3$.
3. Second Iteration:
   • Condition: r() is evaluated. Returns $3$ (non-zero, so true). num becomes $2$.
   • Body: printf("%d", r()) is executed. r() returns $2$ and num becomes $1$. This prints 2.
   • Increment: r() is called. Returns $1$. num becomes $0$.
4. Third Iteration:
   • Condition: r() is evaluated. Returns $0$ (zero, so false). num becomes $-1$.
   • The loop terminates.

The printed output is 52, which corresponds to option B.