GATE 2021 CS (CS2) – Question 45
Which statement about this C program is correct?
#include <stdio.h>
#include <stdlib.h>
struct Node { int value; struct Node *next; };
int main() {
struct Node *boxE,*head,*boxN; int index=0;
boxE=head=(struct Node*)malloc(sizeof(struct Node));
head->value=index;
for(index=1;index<=3;index++) {
boxN=(struct Node*)malloc(sizeof(struct Node));
boxE->next=boxN; boxN->value=index; boxE=boxN;
}
for(index=0;index<=3;index++) {
printf("Value at index %d is %d\n",index,head->value);
head=head->next;
printf("Value at index %d is %d\n",index+1,head->value);
}
}Practise this question in The GATE Grind →
Show answer and explanation
Correct answer: (D) It dereferences an uninitialized pointer and may cause a runtime error
Explanation
Only four nodes, with values zero through three, are allocated. The last node’s next field is never initialized. On the final print-loop iteration, head=head->next reads that indeterminate pointer, and the following head->value dereferences it. This is undefined behaviour and can fail at runtime. Thus D; the finite loop itself is not infinite.