Official PYQ · 2017Set 1 · Q35RecursionMCQ1 mark

GATE CS 2017 Set 1 Q35 — Recursion

Consider the following two functions.

void fun1(int n) {
    if(n == 0) return;
    printf("%d", n);
    fun2(n - 2);
    printf("%d", n);
}
void fun2(int n) {
    if(n == 0) return;
    printf("%d", n);
    fun1(++n);
    printf("%d", n);
}

The output printed when $\text{fun1}(5)$ is called is

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Answer: A

To find the output of fun1(5), we trace the execution step-by-step. Note the crucial detail in fun2(n): the call fun1(++n) uses the pre-increment operator. This increments the local variable n in fun2 before passing it to fun1, meaning the subsequent printf("%d", n) in fun2 will print this incremented value.

Let's trace the calls from the bottom up (starting from the base case):

fun2(0): Returns immediately (prints nothing).
fun1(2):
- Prints 2
- Calls fun2(0)
- Prints 2
- Output: 22
fun2(1):
- Prints 1
- Increments n to 2 and calls fun1(2) (which outputs 22)
- Prints 2 (the incremented value of n)
- Output: 12222 $\rightarrow$ 1222
fun1(3):
- Prints 3
- Calls fun2(1) (which outputs 1222)
- Prints 3
- Output: 312223
fun2(2):
- Prints 2
- Increments n to 3 and calls fun1(3) (which outputs 312223)
- Prints 3
- Output: 23122233
fun1(4):
- Prints 4
- Calls fun2(2) (which outputs 23122233)
- Prints 4
- Output: 4231222334
fun2(3):
- Prints 3
- Increments n to 4 and calls fun1(4) (which outputs 4231222334)
- Prints 4
- Output: 342312223344
fun1(5):
- Prints 5
- Calls fun2(3) (which outputs 342312223344)
- Prints 5
- Output: 53423122233445

Thus, the final printed output is 53423122233445.

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Published 10 Oct 2026

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