GATE CS 2019 Q.28 (CS Q.18): Functions, Recursion, Scope and Storage Classes

Consider the following C program:

#include <stdio.h>
int jumble(int x, int y){
    x = 2 * x + y;
    return x;
}
int main(){
    int x = 2, y = 5;
    y = jumble(y, x);
    x = jumble(y, x);
    printf("%d \n", x);
    return 0;
}

The value printed by the program is ________.

Your answer

Official answer and solution

Official answer: 26
From: Official GATE 2019 answer key

Solution

Trace the function calls and values step by step in C.

The function jumble(int x, int y) is defined as:

int jumble(int x, int y){
    x = 2 * x + y;
    return x;
}

Note that parameters are passed by value, so modifications to x inside jumble do not affect the variables in the caller.

In main():

Initially, $x = 2$ and $y = 5$ .
Execute y = jumble(y, x):
- Argument passed for parameter x is $y = 5$ .
- Argument passed for parameter y is $x = 2$ .
- Inside jumble: $x = 2 \times 5 + 2 = 12$ .
- The function returns $12$ .
- In main, $y$ is assigned $12$ . (At this point, $x = 2, y = 12$ ).
Execute x = jumble(y, x):
- Argument passed for parameter x is $y = 12$ .
- Argument passed for parameter y is $x = 2$ .
- Inside jumble: $x = 2 \times 12 + 2 = 26$ .
- The function returns $26$ .
- In main, $x$ is assigned $26$ .
printf("%d \n", x) prints the value of $x$ , which is $26$ .

Final answer

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

Source

Paper: GATE 2019 Computer Science and Information Technology (CS)
Question: 28 of 65, printed as CS Q.18
Section: Computer Science and Information Technology

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