Computer Knowledge — MCQ Practice Questions & Answers

Question 1

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

Accepted Answer

Correct answer: D. Undefined behavior — 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.

Answer

A. 11

Answer

B. 12

Answer

C. 13

Question 2

What is the difference between scanf() and gets() functions?

Accepted Answer

Correct answer: A. scanf() can read formatted input while gets() reads only strings — 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.

Answer

B. gets() is safer than scanf()

Answer

C. There is no difference

Answer

D. scanf() stops at whitespace while gets() doesn't

Question 3

What is the correct way to allocate memory for a single integer using malloc()?

Accepted Answer

Correct answer: D. Both A and B — 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.

Answer

A. int *ptr = (int *)malloc(sizeof(int));

Answer

B. int *ptr = malloc(sizeof(int));

Answer

C. int *ptr = (int *)malloc(4);

Question 4

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

Accepted Answer

Correct answer: A. 5 5 — *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.

Answer

B. Address Address

Answer

C. Garbage value 5

Answer

D. Compilation error

Question 5

What happens when you use the strcpy() function without bounds checking?

Accepted Answer

Correct answer: B. It may cause buffer overflow if source string is longer than destination — 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.

Answer

A. It prevents buffer overflow automatically

Answer

C. It returns an error code

Answer

D. It truncates the source string automatically

Question 6

What is the output of the following C code? int arr[] = {10, 20, 30}; int *ptr = arr; printf("%d", *(ptr + 1));

Accepted Answer

Correct answer: B. 20 — ptr points to arr[0]. ptr + 1 points to arr[1]. *(ptr + 1) dereferences to get the value at arr[1] which is 20. Pointer arithmetic adds sizeof(int) to the address for each increment.

Answer

A. 10

Answer

C. 30

Answer

D. Address of second element

Question 7

Which of the following correctly describes the scope of a static variable declared inside a function?

Accepted Answer

Correct answer: A. Local to the function, retains value between function calls — A static variable declared inside a function has local scope (visible only within that function) but persists for the entire program lifetime. Its value is retained between function calls and is initialized only once.

Answer

B. Global scope, initialized once

Answer

C. Local to the file only

Answer

D. Creates a new instance on each function call

Question 8

What will be the output of the following C code? int x = 10; int y = 20; int z = x < y ? x++ : y++; printf("%d %d %d", x, y, z);

Accepted Answer

Correct answer: B. 11 20 10 — Step 1: Evaluate condition x < y → 10 < 20 → true. Step 2: Execute true branch: x++ returns 10, then x becomes 11. Step 3: z = 10. Step 4: printf prints x=11, y=20, z=10.

Answer

A. 10 20 10

Answer

C. 10 21 20

Answer

D. 11 21 10

Computer Knowledge - MCQ Practice Questions