Pointers in C Language: 20 flashcards
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1. What is a pointer in C?
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A variable that holds a memory address.
2. Which operator returns the address of a variable?
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The `&` (address-of) operator.
3. What does the `*` operator do when applied to a pointer?
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Dereferences it — accesses the value stored at the address.
4. How do you declare a pointer to an int?
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`int *p;`
5. What does an array name decay to in most expressions?
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A pointer to its first element.
6. How far does `p + 1` advance for an `int *p` when `int` is 4 bytes?
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4 bytes — pointer arithmetic is type-sized.
7. Why pass a pointer to a function?
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So the function can modify the caller's variable or avoid copying large data.
8. Why does `scanf` need `&x`?
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It needs the address to store the input into `x`.
9. What does `malloc` return?
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A pointer to heap memory (or `NULL` on failure).
10. What must you do with memory from `malloc`?
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`free` it to avoid memory leaks.
11. What is a null pointer?
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A pointer that points to nothing (`NULL`); check before dereferencing.
12. What happens when you dereference an uninitialized or invalid pointer?
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Undefined behavior — often a crash.
13. What does `int **pp;` declare?
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A pointer to a pointer to an int.
14. What is a dangling pointer?
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A pointer that still holds the address of memory already freed.
15. Does `int *a, b;` declare two pointers?
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No — `a` is a pointer, `b` is an int. Use `int *a, *b;`.
16. What does `sizeof(arr)` give versus `sizeof(ptr)`?
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`sizeof(arr)` gives total array size; `sizeof(ptr)` gives pointer size.
17. What is the difference between `*p = &x;` and `p = &x;`?
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`*p = &x;` is a type error (stores address into int); `p = &x;` is correct.
18. What do function pointers enable?
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Callbacks and dynamic dispatch.
19. Why are pointers essential for linked lists and trees?
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They link elements by address, enabling dynamic structures.
20. Is pointer arithmetic valid outside the same array?
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No — only within the same array or one past the end.
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