Computer Knowledge - MCQ Practice Questions

Attempting to dereference a NULL pointer causes undefined behavior, typically resulting in a segmentation fault (runtime error). A NULL pointer doesn't point to valid memory.

The correct syntax for declaring a pointer to an integer is 'int *ptr;' where the asterisk (*) indicates it is a pointer variable.

sizeof(int) returns the size of integer in bytes as an integer value. On most modern systems, this is 4 bytes, and printf with %d will print this numeric value.

Both syntaxes are valid in C. Option A explicitly specifies both dimensions, while Option B lets the compiler calculate the first dimension based on initialization.

When a character is printed using %d format specifier, its ASCII value is printed. The ASCII value of 'A' is 65.

In C, an identifier cannot start with a digit. It must start with a letter (a-z, A-Z) or underscore (_). Option B violates this rule by starting with a digit.

Step 1: x=5. Step 2: ++x makes x=6 (pre-increment, used immediately). Step 3: y = 6 + x++ = 6 + 6 = 12. Step 4: x++ increments x to 7 after use. Final: x=7, y=12.

In C, single quotes (') are used for single character constants (char type), while double quotes (") are used for string literals (array of characters ending with null terminator).

This is XOR swap algorithm. Step 1: a = 10^20. Step 2: b = (10^20)^20 = 10. Step 3: a = (10^20)^10 = 20. Result: a=20, b=10 (values are swapped).

fgets() is the safe way to read strings including spaces. scanf("%s") stops at whitespace, gets() is deprecated and unsafe due to buffer overflow risks.

A static variable inside a function is initialized only once and retains its value between successive function calls. It has memory allocated in the data segment, not the stack.

Both are valid syntax. Option A declares an anonymous structure with immediate variable instantiation. Option B declares a named structure type that can be used later to create variables.

The volatile keyword tells the compiler that a variable's value may change unexpectedly (e.g., due to hardware, interrupts, or other threads), preventing compiler optimizations that assume the value doesn't change.

When ptr points to the array arr, ptr[1] is equivalent to *(ptr+1), which accesses the second element of the array, which is 2.

The increment (++) and decrement (--) operators have the highest precedence among all operators in C, followed by unary operators, then multiplicative, additive, and so on.

The 'break' statement is used to exit or terminate a loop or switch statement immediately. It transfers control to the statement following the loop or switch.

The while loop starts with i=0. It prints 0, then increments i to 1, prints 1, increments to 2, prints 2, increments to 3, and the condition i<3 becomes false, so the loop terminates. Output: 0 1 2

The free() function is used to deallocate memory that was previously allocated using malloc(), calloc(), or realloc(). This prevents memory leaks.

This declaration creates a pointer to an integer and initializes it to NULL, which means it doesn't point to any valid memory address. This is a safe initialization practice.

Since both 5 and 2 are integers, integer division is performed: $\frac{5}{2}$ = 2. The %f format specifier then prints this integer value (2) as a floating-point number: 2.000000