Computer Knowledge — MCQ Practice Questions & Answers

Question 1

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.

Answer

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

Answer

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

Answer

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

Question 2

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.

Answer

A. Queue

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C. Heap

Answer

D. Linked List

Question 3

What is the output of the following C code? int x = 5; printf("%d", x++);

Accepted Answer

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

Answer

A. 6

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C. Compilation error

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D. Undefined behavior

Question 4

Which of the following is the correct syntax to declare a pointer in C?

Accepted Answer

Correct answer: A. int *ptr; — In C, pointers are declared using the asterisk (*) symbol before the variable name. The syntax is 'datatype *pointer_name;'

Answer

B. int& ptr;

Answer

C. int ^ptr;

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D. int @ptr;

Question 5

What will be the size of the following array in bytes? char arr[10];

Accepted Answer

Correct answer: A. 10 bytes — Each char occupies 1 byte in memory. An array of 10 chars will occupy 10 × 1 = 10 bytes.

Answer

B. 20 bytes

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C. 40 bytes

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D. 5 bytes

Question 6

What is the purpose of the 'void' keyword in C?

Accepted Answer

Correct answer: C. Both A and B — 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.

Answer

A. To declare a function that returns nothing

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B. To declare a generic pointer

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D. To declare empty variables

Question 7

What is the output of the following C code? int a = 10, b = 20; int c = (a > b) ? a : b; printf("%d", c);

Accepted Answer

Correct answer: B. 20 — 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.

Answer

A. 10

Answer

C. Compilation error

Answer

D. 30

Question 8

What does the strlen() function return?

Accepted Answer

Correct answer: B. Number of characters in a string excluding null terminator — strlen() returns the length of a string without counting the null terminator ('\0'). For example, strlen("hello") returns 5, not 6.

Answer

A. Number of characters in a string including null terminator

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C. Size of memory allocated to string

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D. Address of the first character

Computer Knowledge - MCQ Practice Questions