Need to practice your C programming skills for an upcoming job interview? Try solving these C interview questions that test knowledge of C programming concepts such as arrays, recursion, pointers, memory management, and other skills. We’ll provide feedback on your answers, and you can use a hint if you get stuck.

These C interview questions are examples of real tasks used by employers to screen job candidates such as C developers, software engineers, back-end developers, and others that require knowledge of the C programming language.

**1. Words**

Implement function *sort_words* that sorts an array of words that contain lowercase characters from english alphabet, in descending order, and is **efficient** with respect to time used.

For example, the array *{ "cherry", "orange", "apple" }* should, after sorting, become { "orange", "cherry", "apple" }.

- Example case: Wrong answer
- Several words: Wrong answer
- Performance test on a dictionary: Time limit exceeded

**2. Binary Search Tree**

Binary search tree (BST) is a binary tree where the value of each node is larger or equal to the values in all the nodes in that node's left subtree and smaller than the values in all the nodes in that node's right subtree.

Write a function that, **efficiently** with respect to time used, returns 1 if a given binary search tree contains a given value, else 0.

For example, for the following tree:

- n1 (Value: 1, Left: null, Right: null)
- n2 (Value: 2, Left: n1, Right: n3)
- n3 (Value: 3, Left: null, Right: null)

Call to *contains(&n2, 3)* should return 1 since a tree with root at n2 contains number 3.

- Example case: Wrong answer
- Correctness: Wrong answer
- Performance test on a large tree: Time limit exceeded

**3. Inspect Bits**

Implement the *inspect_bits* function that checks if given number contains 2 or more consecutive ones in its binary representation. If it does, the function should return *1*. Otherwise, it should return *0*.

For example, *inspect_bits(13)* should return *1* as it contains 2 consecutive ones in its binary representation (1101).

**4. Quadratic Equation**

Implement the function *find_roots* to find the roots of the quadratic equation: ax^{2} + bx + c = 0. If the equation has only one solution, the function should return that solution as both roots. The equation will always have at least one solution.

The roots of the quadratic equation can be found with the following formula:

For example, the roots of the equation 2x^{2} + 10x + 8 = 0 are -1 and -4.

**5. Watched Videos**

Implement the *count_views *function. It accepts an array of pointers to the *Viewer *struct, the size of the array, and the character array with the video name. It should return the number of *Viewers *who have watched a *Video* with the *name video_name*.

For example,

```
Video videos[] = { {.name = "Soccer", .unique_views = 500},
{.name = "Basketball", .unique_views = 1000} };
Viewer viewer = {.username = "Dave", .watched_videos = videos,
.watched_videos_size = 2};
Viewer *viewers[] = { &viewer };
```

calling *count_views(viewers, 1, "Soccer")* should return 1.

- Example case: Wrong answer
- Some people did not see the video: Wrong answer
- Various people and videos: Wrong answer
- Strings are dynamically allocated: Wrong answer

**6. User Info**

Consider the struct *UserInfo*, which is used in a performance critical sub-system.

Currently, on a system where an int takes 4 bytes, char takes 1 byte and long long takes 8 bytes, the struct takes 40 bytes of space. Rearrange the struct, without removing, renaming, or changing the type of the members, so that it uses less memory. The code uses pointers to struct members, so struct should be properly aligned.

- The UserInfo struct takes less than 40 bytes of memory: Wrong answer
- The UserInfo struct takes less than 25 bytes of memory: Wrong answer
- The UserInfo struct is properly aligned: Wrong answer

Embedded Systems and C Online Test (Easy)