GATE CS 2025 Set 1 Q.63: Data Types, Operators and Control Flow

Consider the following C program:

#include <stdio.h>
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)

Your answer

Official answer and solution

Official answer: 46
From: Official GATE 2025 answer key

Solution

Trace how t extracts the decimal digits of 14362 from left to right while turn alternates between 0 and 1.

For n = 14362:

The first while (n >= t) t *= 10; loop stops at t = 100000, and t /= 10; sets t = 10000.
The second while (t > 0) loop extracts the digits of 14362 from most significant to least significant (d = 1, 4, 3, 6, 2) while turn starts at 0 and toggles 0, 1, 0, 1, 0:
- d = 1 (turn = 0): ignored; turn becomes 1.
- d = 4 (turn = 1): newnum = 4; turn becomes 0.
- d = 3 (turn = 0): ignored; turn becomes 1.
- d = 6 (turn = 1): newnum = 10*4 + 6 = 46; turn becomes 0.
- d = 2 (turn = 0): ignored; turn becomes 1.
gate(14362) returns 46.

Final answer

The answer is the one in the official GATE answer key. The solution is this site's own explanation.

Source

Paper: GATE 2025 Computer Science and Information Technology - Session 1 (CS1)
Question: 63 of 65
Section: Computer Science and Information Technology

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