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.

By the C standard, sizeof(char) is always 1 byte. A char is the smallest addressable unit in C and is defined to be 1 byte.

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.

The loop initializes i to 0 and continues while i < 5. Values of i: 0, 1, 2, 3, 4. After i becomes 5, the condition is false, so the loop executes 5 times.

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 += operator is a compound assignment operator. x += 3 is equivalent to x = x + 3. Therefore, 5 + 3 = 8.

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).