C Language | Set 7

Following questions have been asked in GATE CS 2010 exam.

1. What does the following program print?

#include<stdio.h> void f(int *p, int *q) {   p = q;  *p = 2; } int i = 0, j = 1; int main() {   f(&i, &j);   printf("%d %d \n", i, j);   getchar();   return 0; }

(A) 2 2
(B) 2 1
(C) 0 1
(D) 0 2

Answer (D)
See below f() with comments for explanation.

/* p points to i and q points to j */ void f(int *p, int *q) {   p = q;    /* p also points to j now */  *p = 2;   /* Value of j is changed to 2 now */ }

2. What is the value printed by the following C program?

#include<stdio.h> int f(int *a, int n) {   if(n <= 0) return 0;   else if(*a % 2 == 0) return *a + f(a+1, n-1);   else return *a - f(a+1, n-1); }   int main() {   int a[] = {12, 7, 13, 4, 11, 6};   printf("%d", f(a, 6));   getchar();   return 0; }

(A) -9
(B) 5
(C) 15
(D) 19

Answer (C)
f() is a recursive function which adds f(a+1, n-1) to *a if *a is even. If *a is odd then f() subtracts f(a+1, n-1) from *a. See below recursion tree for execution of f(a, 6).
.

 f(add(12), 6) /*Since 12 is first element. a contains address of 12 */
    |
    |
 12 + f(add(7), 5) /* Since 7 is the next element, a+1 contains address of 7 */
        |
        |
     7 - f(add(13), 4)
              |
              |
           13 - f(add(4), 3)
                     |
                     |
                  4 + f(add(11), 2)
                             |
                             |
                           11 - f(add(6), 1)
                                    |
                                    |
                                 6 + 0

So, the final returned value is 12 + (7 – (13 – (4 + (11 – (6 + 0))))) = 15

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