Interview Questions for Solidity

The demand for IT professionals and programmers to develop all types of blockchain and crypto-applications has surged as the popularity of blockchain technology and the world of cryptocurrencies has skyrocketed in recent years. This is where the demand for a blockchain developer grows, as smart-contract development is an important aspect of ensuring that players in the blockchain business fulfil their responsibilities.


Job Opportunities for Blockchain Developers

Consider the popularity of initial coin offerings (ICOs). Their history dates back to 2013, when Mastercoin had its first initial coin offering (ICO). In just three years, 54 large ICOs raised around $103 million in 2016, and a year later, this figure had risen to $1.25 billion!

btxchange.io is the source of this information.


There were 92 big projects in 2017, with an even larger number of less well-known ones. Check out the greatest ICOs to see which projects are the most successful at raising funds. The demand for blockchain developers is clear: each project requires safe, secure, and hack-resistant code to run on the blockchain platform, hence each ICO needed to engage numerous smart-contract and blockchain developers.


Furthermore, blockchain developer jobs are in high demand because qualified professionals are hard to come by. This is due to the fact that this is one of the most difficult positions to fill.


In 2017, blockchain developer jobs were the second most sought after. The following graph depicts recent blockchain job postings:



Description of a Blockchain Developer: Required Skills and Qualities

Every project or business wants to engage a knowledgeable and professional blockchain engineer. But how can you tell who he or she is? It is critical to emphasise that, while programming knowledge is essential and a degree in blockchain development is desirable, other factors, such as personal characteristics, are as significant. Working as a blockchain engineer necessitates the ability to collaborate, advise, and communicate with coworkers, as well as the capacity to be responsible and take initiative. Let's go over the most important abilities and attributes a developer should have:


  • good understanding of IT, programming languages, and SC development, as well as the ability to write code independently and solve difficulties

  • the ability to work in a team and collaborate with others; the ability to be self-critical, acknowledge one's own flaws, and provide solutions

  • the capacity to explain and justify why particular difficulties or limits arise in code, as well as how to cope with them

  • a person with an outgoing attitude who is simple to deal with when it comes to accountability, productivity, and honesty

It's also worth noting that observing the candidate at work gives some information about him or her. As a result, during an interview (test task), an employer can observe how an applicant manages his or her time, solves problems, overcomes challenges, and so on.


In addition to talents and attributes, a blockchain developer CV is an important factor to consider. The candidate's education, employment experience, programme expertise, and personal attributes should all be included in the resume. It should be well-structured and smartly written, as it will serve as the candidate's initial impression.


Interview Mistakes You Should Avoid

To begin, it is important to note that everyone makes mistakes. Some of them can even be useful if a candidate recognises and corrects his or her mistakes immediately away. Other errors can be critical, leading to failure.


The most common mistakes made by developer applicants, according to the computer science portal GeeksforGeeks, are:

  • insufficient planning

  • ineffective communication skills

  • not being excited

  • spending time to think instead of communicating through the process

  • making code blunders on the whiteboard

This is a fact! A smart developer, of course, understands what he or she is doing. Although s/he most likely knows how to code well and does an excellent job, things can go wrong during an interview.


Poor preparation does not imply that a person isn't knowledgeable about the subject; it just indicates that he or she did not take the time to review the material and be prepared to respond quickly and rationally. Another common blunder that can be avoided is poor communication. The interviewer wants to talk with the candidate, hear what he or she has to say, and understand how the applicant thinks. This is why it is critical to be approachable and responsive. It's preferable to walk the interviewer through the thinking process rather than taking several minutes to come up with a ready answer. It's also crucial to be excited. If you really want the job, don't be afraid to show it.


Finally, but certainly not least, code errors. Of course, not every interviewer will ask for a whiteboard code sample. Some businesses do, while others simply supply a computer. It's no secret that developers work with a variety of applications, editors, and compilers. Even if the candidate is an expert at what he or she does, coding errors are all too typical when writing on the whiteboard. Here are a few to stay away from:


  • code that is fictitious, incomplete, or unnecessary

  • bad choice of code name or style

  • input data isn't validated.

  • Handwriting is sloppy and difficult to read.

Types of Tasks for Blockchain Developers

It's difficult to give an exact example of a blockchain development test task during an interview. Each firm and employer is distinct, and each operates in a different industry and provides a variety of services and duties.


In general, a developer interview can last up to an hour, with 15 minutes spent to getting to know each other and asking and answering general questions. As a result, time spent creating code can take up to 45 minutes. However, it is important to note that the candidate should not work in silence all of the time — it is in his or her best interests to connect with the interviewer and provide adequate explanations of the process and actions taken.


We'd like to emphasise the importance of generic questions during an interview in this part. Even if some of them are simple, it is critical to remember all of the answers and to define concepts simply by using several examples. This section of the interview demonstrates the candidate's broad knowledge as well as their grasp of current techniques, programmes, and work procedures. It also demonstrates communication and interactive abilities.


Here are some examples of interview questions, along with possible responses:


1. How did you get started developing smart contracts (SCs)?

The demand for smart-contract and blockchain engineers is increasing as the hype surrounding blockchain technologies grows. It is possible to master the Solidity programming language for smart-contract development in a relatively short length of time if you have prior familiarity with IT technologies and computer language coding. Furthermore, the technological requirements for blockchain developers are no more sophisticated or difficult than those for other coding languages. Of course, this isn't a simple effort, but given the many benefits of blockchain and my enthusiasm in innovation, I decided to dedicate myself to mastering SC development.


2. What are the major steps in the development of a SC?

Coding can begin once all of the requirements, such as ERC standards and patterns, have been established. First and foremost, the language should be chosen (Solidity being the most popular).


The contract will then be written or reused in some of the IDEs. Using a framework (Truffle) as a development environment is a good idea.


One of the most crucial stages of SC development is testing. Functional, integrated, and manual testing are examples of different types of testing. There are also other packages that can aid with code style, minor security issues, and test coverage (Solhint, Solium, Solidity coverage).


When all of these procedures are completed, the contract can be deployed to the Ethereum main network.


3. What exactly is a blockchain?

Blockchain is a distributed ledger that is made up of a series of blocks that include cryptographically encrypted records of various transactions. Blockchain delivers security, permanence, transparency, and immutability due to its decentralised nature.


Because all data is recorded and stored in blocks, each of these blocks has specific transaction information. The block also contains references to the previous one in the chain, as well as records on the reward system and unique answers to mathematical puzzles. This is necessary for the mining process to work. This type of design is known as a "block structure," and it might vary due to the fact that it stores a variety of critical data. Here's an example of a block structure:



4. What is the consensus algorithm for the blockchain?

In blockchain operations, consensus algorithms are computational methods that reach agreements on single-data value. The techniques are designed to prevent double-spending in networks with a large number of faulty nodes.


Algorithms include PoW, PoS, DPoS, PoA, PoWeight, BFT, and DAGs, among others. Here are a few examples with descriptions of their characteristics:


Different Types of Consensus Algorithms



5. What distinguishes the Ethereum blockchain from the Bitcoin blockchain?

Ethereum is a public software platform based on the blockchain that allows applications to be deployed without the need for central authority. Ethereum allows you to work for Ether rather than just mine it (as is done in Bitcoin). The Bitcoin blockchain was created with the sole purpose of storing and processing Bitcoin transactions. The ability to run any application code in a decentralised way is one of Ethereum's distinguishing features, whereas Bitcoin, for example, only allows for the usage of one application.


As a result, the Ethereum blockchain does more than just process payments; it also executes smart contracts and runs decentralised applications. Ethereum is frequently employed as a software platform for various startups since it offers a greater range of opportunities.


6. What is the difference between Wei and Ether?

Wei is an Ether unit, or the smallest denomination of Ether, comparable to pennies to pounds or cents to dollars. The following is a chart of unit values:


7. What is a smart contract, and how does it work?

A smart contract (crypto-contract) is a computer software that uses a set of protocols to regulate cryptocurrency transfers and assets between parties based on predetermined circumstances. The code is written by a blockchain user and then executed by a blockchain node. Only if all of the conditions are met does the contract go into effect. SC can be built on Ethereum, NXT, and Chain, with Bitcoin-based automated transactions and scripts. Learn how to rapidly and easily develop smart contracts.


8. What are the several languages that smart contracts can be written in?

A contract can be written in a variety of smart-contract languages (SCL). Let's break down the languages into three groups: Bitcoin, Ethereum, and DSLs.


Languages for Smart Contracts



9. What exactly is Web3.js?

Web3 for Javascript is a set of libraries that allow you to interact with local and remote nodes on the Ethereum blockchain using HTTP/IPC connections.


These libraries provide Web3 objects that enable Ethereum-based applications to interface with the blockchain. Web3 has a lot of functions for keeping track of block data, seeing transaction numbers and balances, and other things. To learn more about the quirks of Web3.js functions, read the insights from the Solidity #3 meetup.


10. Provide some information about the Truffle development environment, including the framework, structure, and migrations.

Truffle is a framework for Ethereum SC development. It was designed for maximum speed and incorporates intelligent optimization for the best outcomes. The following are the characteristics of its structure:


Migrations are JS files that are responsible for task staging and are an important aspect of SC deployment. Migration scripts are developed and recorded through an unique contract on-chain during the project's evolution to ensure that the blockchain continues to evolve.


11. What exactly is EVM?

The Ethereum Virtual Machine (EVM) is a decentralised application platform that executes smart contracts, offers security, and prevents denial-of-service assaults. Many network-connected nodes maintain and run it. EVM is run on all network nodes, and some instructions are executed. EVM also eliminates programme access to each other's status and establishes communication without interference.


12. What effect does the gas restriction and price have on transaction mining?

Certain commands and transactions cost gas to execute because Ethereum transactions are based on gas rather than Ethers. The amount of gas you send (gas price) and a total block gas limit determine this sort of execution. The gas limit is the amount of gas passed along and can be changed by the user who sends the transaction. The gas price is the true transaction cost, which includes both the transaction and execution costs. The transaction price is equal to the amount of gas utilised multiplied by the price of gas.


A transaction's gas limit can affect the amount of time it takes to mine a block. Transactions with high gas restrictions may be treated less favourably and take longer to enter the block.


13. What are the many types of access modifiers available, and how do they differ?

A variety of Solidity function modifiers are available to alter the behaviour of specific functions. They can automatically check function conditions prior to execution. Contract inheritable properties are access modifiers. Functions are classified as follows:

  • external

  • private

  • public

  • internal

Externally, from other contracts, or publically, via messages, these functions differ from one another in terms of call method. It's possible that they'll just allow internal, private access.


14. What is the definition of a fallback method?

When the function signature does not match any other function given in the identifier, or if appropriate data is not supplied, fallback functions are called. When plain Ether is received, functions can also be executed (without any data provided).


15. What are the different sorts of Ethereum networks? What are the distinctions between the two?

Most Ethereum projects are currently conducted on the Ethereum public blockchain, which allows participants, nodes, currencies, and markets to interact. There are three primary types of Ethereum networks, depending on who has access: public, private, and consortium blockchains.


Types of Ethereum Networks


16. What distinguishes libraries from contracts?

Though libraries and contracts are similar in certain ways, libraries can only be used once at a given location. As a result of the DELEGATECALL EVM feature, the library code can be reused. The code executes itself in the contract when library functions are called. Library call functions appear to be the same as base-contract call functions on the surface, however libraries aren't visible in the inheritance tree. In comparison to contracts, library constraints include the absence of state variables, the inability to inherit or be inherited, and the impossibility to accept Ether.


17. DELEGATECALL, STATICCALL, library differences, use cases, and gas prices are all contract interaction elements that should be described.

DELEGATECALL enables the user (delegated the right) to do a variety of storage-related tasks. It's a security risk that ensures the security of contracts sent and received, as well as their storage.


STATICCALL is a new opcode for smart contracts that increases security. It can also call another contract, however any alterations or state changes are disabled during the call.


Libraries perform an important role. They lack a storage option and are unable to hold an Ether. As a result, libraries must be audited before being put into production (with DELEGATECALL, for instance).


The following are examples of library types:

  • static

  • dynamic

  • shared

  • remote

When the code in a library can be accessible throughout the invoking software process, it is referred to as static. A dynamic library differs from a static library in that it can be loaded at run time and linked by a dynamic linker when the application is ready to execute. A shared library (object) is a file that other executable/shared files can use to share it. Remote libraries are used to transfer executables from one computer to another via the internet.


Here's an example of how to use a library:


The cost of gas is determined by the number of instructions, their nature, and the amount of storage available.


18. What is the function of Ecrecover? Please give an example.

Ecrecover yields zero mistakes after recovering public key addresses from an elliptic curved signature.

An example of a function is as follows:

19. Let's talk about memory vs. storage.

Storage and memory are coding terms for storing or saving specific sorts of data, such as arrays or structs. They are two of EVM's three storage locations.


Contract-state variables serve as storage. Each of these contracts has its own persistent storage that is a little pricey to utilise. Within itself, storage may map up to 256-bit words, but it cannot read or write to other storage.


Memory, on the other hand, is used to store temporary data that can be deleted between function calls. It's linear and can address at the byte level, but it's limited to 256 bit width. Memory is also more expensive, depending on the magnitude of the expansion and the quadratic scalability.


20. What is the ERC20 protocol?

The ERC20 token standard defines the many functions and events that must be implemented in an Ethereum token contract. An interface contract declares a set of required functions and events in order to comply with ERC20 specifications. Here's an example of a user interface:


21. What is the ERC721 protocol?

ERC721 is an open, free standard that describes how to create Ethereum tokens. The major distinguishing feature of ERC721 tokens is that they are all one-of-a-kind. These tokens must be maintained, owned, and traded using an interface. Here's an example of a user interface:


22. What are the most prevalent security flaws in SC?

Given the immutability of smart contracts, it is critical to deploy clever code that is free of flaws. It must be safe and secure against potential threats. As a result, the developer must assess the main risks and vulnerabilities that are likely to arise. Among the most important are:


The blockchain developer role is very important in any project development. In order to get this job, one should carefully prepare: revise the material, write a well-structured and comprehensive resume, and increase communication and job-oriented skills.


If you are interested to find out more about ICOs, smart contracts, and blockchain news, visit the Cryptoauxiliary blog. If you have any questions,the team would be more than happy to help you out!



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