Pointers in c language: 17 flashcards
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1. What is a pointer in C?
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A pointer is a variable that stores the memory address of another variable.
2. How do you declare a pointer to an integer?
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`int *ptr;`
3. What does the address-of operator (&) do?
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It returns the memory address of a variable. For example, `&x` gives the address of `x`.
4. What does the dereference operator (*) do when used with a pointer?
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It accesses the value stored at the memory address held by the pointer. For example, `*ptr` gives the value at the address `ptr` points to.
5. Given `int x = 10; int *p = &x;` What is the value of `*p`?
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`*p` is 10, because `p` points to `x` and dereferencing `p` gives the value of `x`.
6. What is a NULL pointer?
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A pointer that is assigned the value `NULL` (or 0) to indicate that it does not point to any valid memory location.
7. Why is it important to initialize a pointer to NULL?
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To avoid undefined behavior from using an uninitialized pointer, which may point to an arbitrary memory location.
8. What is pointer arithmetic?
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Performing arithmetic operations (like addition or subtraction) on pointers. The result is scaled by the size of the data type the pointer points to.
9. If `int arr[5]` and `int *p = arr;` What does `p + 2` point to?
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It points to `arr[2]`, because `p + 2` advances by 2 integers (i.e., 2 * sizeof(int) bytes).
10. What is the relationship between arrays and pointers in C?
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An array name acts as a pointer to its first element. For example, `arr` is equivalent to `&arr[0]`.
11. How do you pass a pointer to a function to modify a variable?
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Pass the address of the variable using `&` and accept it as a pointer parameter. For example: `void func(int *p) { *p = 20; }` and call `func(&x);`.
12. What is a pointer to a pointer?
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A pointer that stores the address of another pointer. Declared as `int **ptr;`.
13. Given `int x = 5; int *p = &x; int **pp = &p;` What is `**pp`?
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`**pp` is 5, because `pp` points to `p`, and `p` points to `x`, so dereferencing twice gives the value of `x`.
14. What is a void pointer (`void *`)?
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A generic pointer that can hold the address of any data type, but cannot be dereferenced directly without casting.
15. How do you dynamically allocate memory for an integer using `malloc`?
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`int *p = (int *)malloc(sizeof(int));`
16. What is a dangling pointer?
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A pointer that points to a memory location that has been freed or deallocated. Using it leads to undefined behavior.
17. What is the difference between `p` and `&p` when `p` is a pointer?
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`p` is the address stored in the pointer (the address of the variable it points to). `&p` is the address of the pointer variable itself.
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