Computer Knowledge - MCQ Practice Questions

Due to memory alignment/padding: int x (4 bytes), char c (1 byte) + 3 bytes padding, int y (4 bytes) = 12 bytes total. The compiler adds padding to align data members to their natural boundaries for efficient memory access.

Both {} and {0} will initialize all array elements to 0. When you provide fewer initializers than array size, remaining elements are automatically set to 0.

A pointer to a pointer is declared using two asterisks (). int ptr declares a pointer that points to another pointer that points to an integer.

Variables declared inside a function have local scope (also called function scope). They are only accessible within that function and are destroyed when the function returns.

calloc() allocates memory and initializes all bytes to 0, takes (number of elements, size of each element). malloc() just allocates memory without initialization and takes total size. calloc() is slightly slower due to initialization.

The correct syntax is FILE *fp = fopen("filename", "mode");. fopen() returns a pointer to a FILE structure, and the mode string specifies how to open the file ("r" for read, "w" for write, etc.).

ptr points to arr[0]. ptr + 2 points to arr[2]. *(ptr + 2) dereferences to get the value at arr[2], which is 3. Pointer arithmetic moves by the size of the data type (integers).

When i = 1, it prints 1. When i = 2, continue skips the printf() and moves to the next iteration. When i = 3, it prints 3. Output: 1 3

x++ is post-increment. First printf uses current value (10), then x is incremented. Second printf uses new value (11). Output: 1011

The correct syntax for declaring a pointer to an integer is 'int *ptr;' where the asterisk (*) indicates that ptr is a pointer. The placement of * before the variable name is crucial.

When %d format specifier is used with a char variable, it prints the ASCII value. The ASCII value of 'A' is 65. If it were 'a', the value would be 97.

malloc() (memory allocation) is the standard function in C for dynamic memory allocation. It returns a void pointer to the allocated memory. The syntax is: ptr = (type*)malloc(size);

Array indexing in C starts from 0. str[0]='H', str[1]='e', str[2]='l', str[3]='l', str[4]='o', str[5]='\0'. Therefore, str[1] is 'e'.

strcmp() is the standard library function used to compare two strings. It returns 0 if strings are equal, negative if first string is less, and positive if first string is greater. It's declared in string.h.

p is a pointer to x, so &x gives the address of x. *p (dereferencing) gives the value stored at that address, which is 5. The output will be 5.

The operator += means x = x + 3. So x = 5 + 3 = 8. The printf statement outputs 8.

The do-while loop executes the loop body at least once before checking the condition. Other loops check the condition before execution. Syntax: do { } while(condition);

The pre-increment operator (++x) increments x first, then assigns it. So x becomes 6, and y is assigned 6. Output: 6 6.

malloc() (memory allocation) is used to dynamically allocate memory on the heap in C. It requires #include <stdlib.h>. new() is used in C++, not C.

This is a swap operation. Initially a=10, b=20. After temp=a (temp=10), a=b (a=20), b=temp (b=10). Output: 20 10.