Computer Knowledge — MCQ Practice Questions & Answers

Question 1

What will be the output of the following C code? int main() { int x = 5; int *p = &x; int **q = &p; printf("%d", **q + 1); return 0; }

Accepted Answer

Correct answer: A. 6 — The correct answer is 6 because **q is a pointer to pointer that points to p, which points to x. When we dereference **q, we get the value of x (which is 5), and then adding 1 gives us 6, which is printed. The key concept here is understanding pointer dereferencing: a single asterisk dereferences one level, so double asterisks dereference two levels, bringing us from q to p to the actual value stored in x. Any other answer would be incorrect because it would either misunderstand the double dereferencing operation or incorrectly interpret what value is being accessed—for instance, if someone only dereferenced once or forgot to add 1, they would get a different result.

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B. 5

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C. Compilation error

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D. Garbage value

Question 2

Which of the following correctly describes the difference between malloc() and calloc() in C?

Accepted Answer

Correct answer: B. calloc() initializes memory to zero and takes two arguments (number of elements and size), malloc() takes one argument and does not initialize — The answer is correct because it accurately captures the fundamental distinction between these two memory allocation functions in C. malloc() allocates a block of uninitialized memory and requires only the total number of bytes as a single argument, while calloc() allocates memory for an array of elements, takes two arguments (number of elements and size per element), and crucially initializes all allocated memory to zero. This initialization feature of calloc() is a key advantage when you need guaranteed zero values, whereas malloc() leaves memory with whatever garbage values were previously there. Other options would be incorrect if they claimed malloc() initializes memory, if they stated calloc() takes only one argument, or if they reversed which function initializes to zero.

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A. malloc() initializes memory to zero, calloc() does not

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C. malloc() is faster than calloc() but uses more memory

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D. calloc() can only allocate memory for arrays, malloc() can allocate for any data type

Question 3

What is the output of the following code snippet? int main() { char arr[] = "GATE"; char *p = arr; printf("%d
", sizeof(arr)); printf("%d", sizeof(p)); return 0; }

Accepted Answer

Correct answer: C. 5 and 8 (on 64-bit system) — The output is 5 and 8 because sizeof(arr) returns 5 bytes (4 characters plus 1 null terminator in the string "GATE"), while sizeof(p) returns 8 bytes on a 64-bit system since p is a pointer variable and pointers occupy 8 bytes in 64-bit architecture. The key concept is that sizeof() behaves differently for arrays versus pointers: when applied to an array, it returns the total memory allocated for the entire array, but when applied to a pointer, it only returns the size of the pointer itself, not what it points to. Other options would be incorrect because they either miscalculate the array size by forgetting the null terminator, use incorrect pointer sizes (like 4 bytes for 32-bit systems), or confuse the size of the array with the size of the pointer variable.

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A. 4 and 4

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B. 5 and 4

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D. 4 and 8 (on 64-bit system)

Question 4

Consider a structure with bit fields. What will be the size of the following structure in bytes? struct demo { unsigned int a : 5; unsigned int b : 3; unsigned int c : 4; unsigned int d : 7; };

Accepted Answer

Correct answer: C. 4 bytes — Bit fields in C are packed into the smallest integral type that can accommodate them. Here, a(5) + b(3) + c(4) + d(7) = 19 bits total. Since 19 bits exceed 16 bits but fit within 32 bits, the compiler allocates 4 bytes (32 bits) for this structure, following standard packing rules.

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A. 1 byte

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B. 2 bytes

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D. 8 bytes

Question 5

What is the purpose of the volatile keyword in C?

Accepted Answer

Correct answer: B. To inform the compiler that a variable may change unexpectedly and should not be optimized out or cached in registers — The volatile keyword tells the compiler that a variable's value may change at any time (due to external factors like hardware registers, signal handlers, or multi-threading) and should be read from memory every time it's accessed, rather than being optimized by the compiler or cached in a register.

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A. To prevent a variable from being modified by the program

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C. To allocate memory on the stack instead of the heap

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D. To make a variable accessible across all files in a project

Question 6

Which data structure uses the LIFO (Last In First Out) principle and is commonly used for function call management in programming languages?

Accepted Answer

Correct answer: B. Stack — A Stack follows LIFO principle where the last element inserted is the first one to be removed. It is fundamental in managing function calls through the call stack, undo/redo operations, and expression evaluation. Queues use FIFO, Heaps are used for priority ordering, and Linked Lists maintain sequential but flexible storage.

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A. Queue

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C. Heap

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D. Linked List

Question 7

Which of the following operations has an average time complexity of O(1) in a Hash Table with good hash function and low collision rate?

Accepted Answer

Correct answer: C. Both insertion and search — Hash Tables achieve O(1) average-case time complexity for both insertion and search operations when using a well-designed hash function that minimizes collisions and maintains a good load factor. Deletion also operates in O(1) average time. However, in worst-case scenarios with poor hash functions or high collision rates, these operations can degrade to O(n). The key to performance is maintaining low collision rates through techniques like chaining or open addressing.

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A. Insertion only

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B. Search only

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D. Deletion only

Question 8

In a B-tree of order m, what is the maximum number of children a non-leaf node can have?

Accepted Answer

Correct answer: C. m + 1 — A B-tree of order m has a maximum of m children per node, which means it can have a maximum of (m-1) keys. Each node can have between ⌈m/2⌉ and m children (for non-leaf nodes), ensuring balance. B-trees are commonly used in database indexing and file systems because they minimize disk I/O operations through their multi-level structure and balanced properties.

Answer

A. m

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B. m - 1

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D. 2m

Computer Knowledge - MCQ Practice Questions