Computer Knowledge - MCQ Practice Questions

Array name decays to pointer. p[5] is equivalent to *(p+5) which is *(arr+5) or arr[5]. This demonstrates pointer arithmetic.

Declaration tells the compiler about a variable's name and type (e.g., 'extern int x;'). Definition actually allocates memory (e.g., 'int x = 5;'). A variable can be declared multiple times but defined only once.

Uninitialized local variables contain garbage values (unpredictable values from previous memory contents). Global and static variables are automatically initialized to 0, but local variables are not.

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 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.

getchar() specifically reads a single character from the standard input stream, while scanf("%c", &ch) is a formatted input function. getchar() is more straightforward for reading single characters.

In C, when an array name is used in most contexts, it decays (converts) to a pointer to its first element. For example, in int arr[5];, arr behaves like &arr[0]. However, arrays and pointers are not identical; arrays have fixed size while pointers are variables.

A function declaration (or prototype) tells the compiler about the function's name, return type, and parameters. A function definition includes the declaration along with the function body containing the actual implementation. Declaration is optional if the function is defined before use.

The correct syntax for a function pointer is: int (*ptr)(int, int);. The parentheses around (*ptr) are necessary to indicate that ptr is a pointer to a function, not a function returning a pointer. Option A declares a function returning an int pointer.

Only p is declared as a pointer (int *p). The variable q is declared as a regular integer (int q). The * applies only to p in this declaration.

sizeof(s) includes the null terminator '\0'. "hello" has 5 characters + 1 null terminator = 6 bytes. If s was a pointer, sizeof would give pointer size.

Modulus, multiplication, and division have equal precedence (left-to-right): (5 % 2) = 1, then (1 * 3) = 3, then ($\frac{3}{2}$) = 1 (integer division). Answer is 1, not 2. Correction: 1 is correct.

In a union, all members share the same memory location. The size of the union equals the size of the largest member. Only one member can hold a value at a time.

Using <> tells the compiler to search in standard system directories. Using "" tells it to search in the current directory first, then system directories. Generally, "" is used for user-defined headers and <> for standard library headers.

When p points to arr, p[2] is equivalent to *(p+2) and accesses the value at arr[2]. Pointers and array names decay to pointers, and pointer indexing retrieves the value.

malloc() allocates memory in bytes. To allocate for 10 integers, we need 10 * sizeof(int) bytes. Option A allocates only 10 bytes, insufficient for 10 integers.

This expression involves modifying the same variable (x) multiple times without an intervening sequence point. This is undefined behavior in C, and the result cannot be predicted reliably.

This function calculates factorial. func(4) = 4 * func(3) = 4 * (3 * func(2)) = 4 * (3 * (2 * func(1))) = 4 * 3 * 2 * 1 = 24.

XOR operation: 5 ^ 3. Binary: 0101 ^ 0011 = 0110 = 6. XOR returns 1 when bits are different, 0 when same.