GATE2025_CS1_Q63

Consider the following C program:

#include 
int gate (int n) {
  int d, t, newnum, turn;
  newnum = turn = 0; t=1;
  while (n>=t) t *= 10;
  t /=10;
  while (t>0) {
    d = n/t;
    n = n%t;
    t /= 10;
    if (turn) newnum = 10*newnum + d;
    turn = (turn + 1) % 2;
  }
  return newnum;
}
int main () {
  printf ("%d", gate(14362));
  return 0;
}

The value printed by the given C program is ______. (Answer in integer)

✅ Final Answer:

The correct answer is 46.

🔹 Short Answer:

The C program's `gate` function isolates each digit of the input number from left to right. A `turn` variable alternates between 0 and 1. The `if (turn)` condition ensures that only digits from even positions (2nd, 4th, 6th, etc.) are used to build a new number. For the input 14362, the 2nd digit (4) and the 4th digit (6) are selected, forming the number 46, which is printed.

🔸 Long Answer:

To determine the output, we need to trace the execution of the `gate(14362)` function step by step.

Code Analysis

The `gate` function essentially does the following:

1. It determines the place value of the most significant digit of the input `n` and stores it in `t`. For `n = 14362`, `t` will become `10000`.
2. It then iterates through the number digit by digit from left to right.
3. A variable `turn` acts as a flag, toggling between 0 and 1.
4. The line if (turn) means a digit is only appended to `newnum` if `turn` is 1 (i.e., on the 2nd, 4th, 6th... iterations).

Step-by-Step Execution Trace

Let's trace the main `while (t > 0)` loop with the input `n = 14362`.
Initial values before the loop: `newnum = 0`, `turn = 0`, `t = 10000`.

Iteration	`t` (start)	`d = n/t`	`n = n%t`	`turn` (before if)	`if(turn)` fires?	`newnum` (end)	`turn` (end)
1	10000	1	4362	0	No	0	1
2	1000	4	362	1	Yes	10*0 + 4 = 4	0
3	100	3	62	0	No	4	1
4	10	6	2	1	Yes	10*4 + 6 = 46	0
5	1	2	0	0	No	46	1

The loop terminates as `t` becomes 0. The function returns the final value of `newnum`, which is 46.

The `main` function then prints this returned value.

Bibliography:
- Kernighan, B. W., & Ritchie, D. M. (1988). The C Programming Language. Prentice Hall.
- Prata, S. (2014). C Primer Plus. Addison-Wesley Professional.

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