Memory Allocation Questions and Answers

Q: The type of linked list in which the node does not contain any pointer or reference to the previous node:

Correct answer: Singly linked listIn a singly linked list each node holds one pointer, to its successor. Nothing refers backwards, so traversal runs in one direction only and deleting a node requires a reference to the one before it.Adding a second pointer to the predecessor gives a doubly linked list, which costs memory per node but allows backward traversal and deletion given only the target node. Whether a list is circular is a separate question, concerning only whether the last node points back to the first.

Q: malloc() returns a NULL if it fails to allocate the requested memory.

Correct answer: TRUEWhen malloc cannot satisfy a request it returns a null pointer. That is the only way it reports failure - there is no error code and nothing is set beyond, on most systems, errno.Checking the return value is therefore the caller's responsibility, and omitting the check is a common fault: the program proceeds to dereference a null pointer and crashes at a line some distance from the real cause. Note that malloc(0) may legitimately return either null or a unique pointer.

Q: Which of the following will return a result most quickly for searching a given key?

Correct answer: Binary Search TreeA balanced binary search tree finds a key in \( O(\log n) \) comparisons, halving the search space at each step.An unsorted array and a sorted linked list both require \( O(n) \), the list because it cannot be indexed and so cannot be bisected however well ordered it is. A sorted array also permits binary search at \( O(\log n) \), so the two are comparable on lookup - but the tree keeps that performance while supporting insertion and deletion in \( O(\log n) \), where the array would need elements shifted.

Q: What is the correct sequence of the compilation Process −

Correct answer: Preprocessor, Compiler, Assembler, LinkingThe order follows what each stage needs from the last. The preprocessor runs first, handling #include, #define and conditional compilation to produce a single translation unit of pure C.The compiler turns that into assembly, the assembler turns assembly into an object file of machine code with unresolved references, and the linker joins the object files and libraries into an executable, resolving those references. A missing function is a link error precisely because the linker is the first stage that looks across files.

Q: Why do we write (int *) before malloc? int *ip = (int *)malloc(sizeof(int));

Correct answer: It is for the type-castingThe cast converts the void * that malloc returns to an int *. It tells the compiler how to treat the value; malloc itself never sees it and learns nothing about the intended type.In C the cast is unnecessary, since void * converts implicitly to any object pointer type, and it can do harm: if stdlib.h has been forgotten, the compiler assumes a return type of int, and the cast silences the very warning that would have exposed the problem. In C++ it is required.

Q: Specify the 2 library functions to dynamically allocate memory?

Correct answer: malloc() and calloc()malloc and calloc are the two allocation functions in standard C. malloc takes a single total size and leaves the block uninitialised; calloc takes a count and an element size and zeroes the result.The standard library also provides realloc to resize an existing block and free to release one, so four functions in all - but only two of them allocate fresh storage. The others named in the options are not standard C at all.

Q: If malloc() successfully allocates memory it returns the number of bytes it has allocated.

Correct answer: FALSEmalloc returns a pointer to the allocated block, not a count of bytes. On success it is the address of the storage; on failure it is null.The number of bytes is what the caller supplied as the argument, so returning it would convey nothing. There is in fact no portable way to ask how large an allocated block is once it has been made, which is why programs that need to know must record the size themselves alongside the pointer.

91.

The type of linked list in which the node does not contain any pointer or reference to the previous node:

A.Circularly singly linked list
B.Singly linked list
C.Circular doubly linked list
D.Doubly linked list

Answer: B

Correct answer: Singly linked list

In a singly linked list each node holds one pointer, to its successor. Nothing refers backwards, so traversal runs in one direction only and deleting a node requires a reference to the one before it.

Adding a second pointer to the predecessor gives a doubly linked list, which costs memory per node but allows backward traversal and deletion given only the target node. Whether a list is circular is a separate question, concerning only whether the last node points back to the first.

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92.

malloc() returns a NULL if it fails to allocate the requested memory.

A.TRUE
B.FALSE
C.May Be
D.Can't Say

Answer: A

Correct answer: TRUE

When malloc cannot satisfy a request it returns a null pointer. That is the only way it reports failure - there is no error code and nothing is set beyond, on most systems, errno.

Checking the return value is therefore the caller's responsibility, and omitting the check is a common fault: the program proceeds to dereference a null pointer and crashes at a line some distance from the real cause. Note that malloc(0) may legitimately return either null or a unique pointer.

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93.

A memory leak in a C program occurs when ________.

A.a pointer is dereferenced after being freed
B.allocated memory is never released and its pointer is lost
C.an array is indexed beyond its bounds
D.two pointers refer to the same block

Answer: A

Correct answer: allocated memory is never released and its pointer is lost

A leak is memory that remains allocated while the program has no pointer left with which to free it. The block stays reserved for the life of the process, and in a long-running program repeated leaks exhaust the heap.

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94.

Which of the following will return a result most quickly for searching a given key?

A.Unsorted Array
B.Sorted Array
C.Sorted linked list
D.Binary Search Tree

Answer: D

Correct answer: Binary Search Tree

A balanced binary search tree finds a key in \( O(\log n) \) comparisons, halving the search space at each step.

An unsorted array and a sorted linked list both require \( O(n) \), the list because it cannot be indexed and so cannot be bisected however well ordered it is. A sorted array also permits binary search at \( O(\log n) \), so the two are comparable on lookup - but the tree keeps that performance while supporting insertion and deletion in \( O(\log n) \), where the array would need elements shifted.

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95.

What is the correct sequence of the compilation Process −

A.Assembler, Compiler, Preprocessor, Linking
B.Compiler, Assembler, Preprocessor, Linking
C.Preprocessor, Compiler, Assembler, Linking
D.Assembler, Compiler, Linking, Preprocessor

Answer: C

Correct answer: Preprocessor, Compiler, Assembler, Linking

The order follows what each stage needs from the last. The preprocessor runs first, handling #include, #define and conditional compilation to produce a single translation unit of pure C.

The compiler turns that into assembly, the assembler turns assembly into an object file of machine code with unresolved references, and the linker joins the object files and libraries into an executable, resolving those references. A missing function is a link error precisely because the linker is the first stage that looks across files.

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96.

Why do we write (int *) before malloc?
int *ip = (int *)malloc(sizeof(int));

A.It is for the syntax correctness
B.It is for the type-casting
C.It is to inform malloc function about the data-type expected
D.None of the mentioned

Answer: B

Correct answer: It is for the type-casting

The cast converts the void * that malloc returns to an int *. It tells the compiler how to treat the value; malloc itself never sees it and learns nothing about the intended type.

In C the cast is unnecessary, since void * converts implicitly to any object pointer type, and it can do harm: if stdlib.h has been forgotten, the compiler assumes a return type of int, and the cast silences the very warning that would have exposed the problem. In C++ it is required.

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97.

Point out the error in the following program.

#include <stdio.h>
#include <stdlib.h>

int main()
{
    int *a[3];
    a = (int*) malloc(sizeof(int)*3);
    free(a);
    return 0;
}

A.Error: unable to allocate memory
B.Error: We cannot store address of allocated memory in a
C.Error: unable to free memory
D.No error

Answer: B

Correct answer: Error: We cannot store address of allocated memory in a

int *a[3] declares an array of three pointers. An array name is not a modifiable lvalue, so the compiler rejects any assignment to a.

What the code appears to intend is int *a;, a single pointer able to hold the returned address. The parentheses make all the difference in such declarations, and reading them from the identifier outwards - a is an array of 3 pointers to int - is the reliable technique.

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98.

Specify the 2 library functions to dynamically allocate memory?

A.malloc() and memalloc()
B.alloc() and memalloc()
C.malloc() and calloc()
D.memalloc() and faralloc()

Answer: C

Correct answer: malloc() and calloc()

malloc and calloc are the two allocation functions in standard C. malloc takes a single total size and leaves the block uninitialised; calloc takes a count and an element size and zeroes the result.

The standard library also provides realloc to resize an existing block and free to release one, so four functions in all - but only two of them allocate fresh storage. The others named in the options are not standard C at all.

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99.

In the call calloc(n, size), what do the two arguments represent ?

A.The total bytes and an alignment value
B.The number of elements and the size of each element
C.The starting address and the length
D.The size in bytes and an initialisation value

Answer: A

Correct answer: The number of elements and the size of each element

calloc() multiplies the two arguments to find the total number of bytes, then clears them. Splitting the request in two lets the library detect an overflow in that multiplication, which a single-argument malloc() call cannot do.

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100.

If malloc() successfully allocates memory it returns the number of bytes it has allocated.

A.TRUE
B.FALSE
C.May Be
D.Can't Say

Answer: B

Correct answer: FALSE

malloc returns a pointer to the allocated block, not a count of bytes. On success it is the address of the storage; on failure it is null.

The number of bytes is what the caller supplied as the argument, so returning it would convey nothing. There is in fact no portable way to ask how large an allocated block is once it has been made, which is why programs that need to know must record the size themselves alongside the pointer.

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