C Online Test

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About the test

The C online test assesses knowledge of programming in the C language through a series of live coding questions.

The assessment includes work-sample tasks such as:

  • Using pointers to reference a location in memory.
  • Implementing and properly using data structures and algorithms.
  • Optimizing memory management and fixing memory leaks.

A good C developer needs a solid understanding of the C programming language and the implications of low-level optimizations to work on complex or performance critical code.

Sample public questions

20 min

Your company is analyzing malware which targets numerical record files.

The malware uses a sliding window over the array of numbers in a file, and tries to match the following pattern:

Tl, -, -, X, -, -, -, Tr

The entire window is moved so that 'X' passes through all the values and is compared to the numbers at the 'Tl' and 'Tr' locations, which are positioned at a constant offset to 'X'.

The malware has the following rules:

  • If the value at the 'Tl' or 'Tr' position of the pattern is bigger or equal to the value at the 'X’ position, the malware replaces the value at 'X' with 0.
  • If the value at the 'Tl' or 'Tr' offset is out of bounds, then the value at 'X' is only compared to the other existing value.
  • The record is processed in two stages: first, all the positions that should be set to 0 are located, using the original values for comparison. Only after all positions have been identified do they get set to 0.

For example, if the values in a record file are the following:

{ 1, 2, 0, 5, 0, 2, 4, 3, 3, 3 }

The expected values after the malware runs are:

{ 1, 0, 0, 5, 0, 0, 0, 3, 3, 0 }

In this example, both '2's, the '4' and the last '3' were replaced by 0.

Implement the simulate function so that the malware behavior is replicated for further study.

30 min
2D Array

A turn-based strategy game has a grid with water and land. The grid contains a true value where it's water and false where it's land.

The player controls a boat unit with a particular movement pattern. It can only move to fixed destinations from its current position as shown in the image below:

movement pattern

The boat can only move in a direct path through water to the possible destinations, so a destination will become unreachable if there is land in the way. 

Implement the can_travel_to function, that checks whether a destination is reachable by the boat. It should return true for destinations that are reachable according to the pattern above, and false for unreachable or out of bounds destinations which are outside the grid. 

For example, consider the following code:

bool game_matrix[6][6] = {
    {false, true,  true,  false, false, false},
    {true,  true,  true,  false, false, false},
    {true,  true,  true,  true,  true,  true},
    {false, true,  true,  false, true,  true},
    {false, true,  true,  true,  false, true},
    {false, false, false, false, false, false},

printf("%d\n", can_travel_to((bool*) game_matrix, 6, 6, 3, 2, 2, 2)); // true, Valid move
printf("%d\n", can_travel_to((bool*) game_matrix, 6, 6, 3, 2, 3, 4)); // false, Can't travel through land
printf("%d\n", can_travel_to((bool*) game_matrix, 6, 6, 3, 2, 6, 2)); // false, Out of bounds

The following image shows valid and invalid destinations when the boat is in the position (3, 2):

terrain movement

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30 more premium C questions

Square, Descriptor, Copy Bit, Max Sum, Init Range, Increment, Internal Nodes, Battery, Strings Pointer, Allocate String, Count Letters, Segment, Read Write Execute, Sort Params, Run in Parallel, Digital Flasks, Planet Search, Shipping, Airport Networks, Company Stock, Flimsy Ladder, Calories Burned, Tiles, Weighted Average, Node, Racer, Chain Link, Paper Strip, Circuit Simulator, Vectors.

Skills and topics tested

  • C
  • Pointers
  • Memory Management
  • Bit Manipulation
  • Algorithmic Thinking
  • Arrays
  • Tree
  • Language
  • Pointer to Pointer
  • Strings
  • Arithmetic
  • Pass by Reference
  • Higher Order Function
  • Multithreading
  • Pthreads
  • Conditions
  • Iteration
  • 2D Array
  • Graphs
  • AI Code Review
  • Conditional Statements
  • Loops
  • Bug Fixing
  • Recursion
  • Synchronization
  • Linked List

For job roles

  • Back-End Developer
  • C Developer

Sample candidate report

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Product reviews

G2 - Crowd Badge
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Capterra - 4.5 Stars
Capterra - Shortlist (2023)

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