Computer Knowledge - MCQ Practice Questions

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.

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.

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.

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.

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.

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.

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.

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.

A Heap (either Min-Heap or Max-Heap) is the optimal data structure for implementing priority queues with O(log n) insertion and deletion time complexity.

In a Max-Heap, the element with the highest priority is always at the root, enabling efficient extraction of the maximum element.

Arrays and Linked Lists would require O(n) time for priority-based operations, while Graphs are unsuitable for this purpose.

Heaps are fundamental in algorithms like Dijkstra's and Prim's for finding shortest paths.

The post-increment operator (x++) returns the current value of x before incrementing. So printf prints 5, and then x becomes 6.

In C, pointers are declared using the asterisk (*) symbol before the variable name. The syntax is 'datatype *pointer_name;'

Each char occupies 1 byte in memory. An array of 10 chars will occupy 10 × 1 = 10 bytes.

void is used in two contexts: (1) as a function return type when a function doesn't return a value, and (2) to declare a generic pointer (void *) that can point to any data type.

The ternary operator (condition ? true_value : false_value) evaluates the condition (a > b). Since 10 is not greater than 20, it returns b which is 20.

strlen() returns the length of a string without counting the null terminator ('\0'). For example, strlen("hello") returns 5, not 6.

This code exhibits undefined behavior because x is modified twice between sequence points without an intervening sequence point. The result depends on the compiler's implementation.

scanf() reads formatted input based on format specifiers and stops at whitespace. gets() reads a string until a newline is encountered. Note: gets() is deprecated due to buffer overflow vulnerabilities.

Both A and B are correct. Option A uses explicit type casting which is optional in C (not in C++). Option B avoids casting. Using sizeof(int) is preferred over hardcoding 4, as int size may vary across systems.

*ptr dereferences the pointer to access the value at the address it points to, which is x = 5. So both *ptr and x print 5.

strcpy() does not perform bounds checking. If the source string is longer than the destination buffer, it will write beyond the buffer boundary, causing a buffer overflow. This is a security vulnerability. Using strncpy() is safer.