Top 20 Solidity Interview Questions and Answers for 2024 | Simplilearn (2024)

Top Solidity Interview Questions and Answers for 2024

1. What is Solidity?

Solidity is a high-level language used in the blockchain ecosystem for implementing smart contracts. Designed specifically for targeting the Ethereum Virtual Machine, Solidity was influenced by several programming languages, such as JavaScript, Python, and C++.

2. What are some important features of Solidity?

Solidity has some salient features, which include libraries, contracts, and inheritance support. With Solidity, users can also create custom data types which can be a crucial part of smart contract development.

3. What types of applications can be developed using Solidity?

Solidity finds its application in creating smart contracts on Ethereum, which is a decentralized platform that is responsible for running smart contracts. Smart contracts function just as programmed and they are not prone to third-party interference. While it is most commonly used for developing smart contracts, you can also develop complex decentralized applications. You can develop various aspects, such as voting systems, crowdfunding platforms, decentralized exchanges, lending platforms, and much more.

4. What are the main differences between Solidity and other programming languages like Python, Java, or C++?

One main difference between Solidity and other programming languages like Python, C++, and Java is their application. While you can create centralized applications using these popular programming languages, Solidity is created to work with the Ethereum Virtual Machine. Therefore, it has certain special features such as creating smart contracts.

5. What is machine code in relation to Solidity contracts?

Machine codes are a compilation of solidity contracts, which are written in a high-level language. And it is the machine code that is executed on the Ethereum blockchain by the computer’s processor. A basic understanding of machine code is needed to understand what Solidity contracts are and how they work.

6. What is an enum? What are the restrictions on their use?

Enums are one of the methods used for creating user-defined types in Solidity. While you can implement an implicit conversion when using enums, they allow explicit conversion both to and from all integer types. Enums require at least one member, and the explicit conversions check the runtime value ranges. When there’s a failure, it results in an exception.

7. What is EVM bytecode?

EVM is the abbreviation for Ethereum Virtual Machine, which is a low-level programming language that is compiled from Solidity— a high-level language. EVM helps reduce the operating system dependency by sitting between the application layer and the operating system. Because of EVM, Ethereum contracts can be on almost any computer.

8. What is a library and how many types are there?

A library is a reusable piece of code that is used by smart contracts. There are two types of libraries, which are deployed and embedded libraries. While deployed libraries have an address of their own and can be used by several other smart contracts, embedded libraries are used by smart contracts wherein they are used as a part of the code. Additionally, embedded libraries do not have their own address.

9. What is the function of the consensus algorithm?

The consensus algorithm is one of the aspects that make decentralization possible for blockchain-powered platforms and applications. Consensus algorithms enable a mechanism that ensures a majority of the token holders and stakeholders agree upon and decide the credibility of a transaction while also deciding how to add new blocks of transactions. Consensus helps prevent the chances of any user making unauthorized changes.

10. What do you understand about the Ethereum network?

The Ethereum network is an open-source blockchain platform that leverages blockchain technology. It is most commonly used for creating decentralized applications that do not depend on a single authority or a centralized entity and instead are monitored by all the peers.

11. What are the differences between Ethereum and blockchain and bitcoin?

The most basic difference between bitcoin and Ethereum is that bitcoin is a cryptocurrency and the latter is a ledger technology that is used to create new programs. Bitcoin was created as an alternative to the national currency while the Ethereum platform was created for programmatic contracts and applications which use its own currency— ETH. While bitcoin transactions might take minutes to be completed, it only takes seconds to complete Ethereum transactions.

12. What are the benefits of using smart contracts on Ethereum?

There are several advantages of using smart contracts on Ethereum over traditional contracts, such as a greater degree of security since smart contracts are stored on the blockchain. This makes these contracts immune to tampering. Since smart contracts are designed to automate various tasks including the transfer of funds and verification of identities, they’re more efficient.

13. What tools can be used for testing Solidity codes?

Some of the most popular and commonly used tools for testing Solidity codes are Solium and Truffle. You can find and fix issues in your Solidity codes with Solium, which is a linter. Truffle can be used as a development environment, asset pipeline, and testing framework for Ethereum.

14. Is it possible to use loops in Solidity?

Yes, you can use loops in Solidity. However, this may come with certain restrictions such as not being able to use a for loop for iterating over an array. One thing to remember is to avoid using infinite loops in Solidity. When you create infinite loops, it results in the loss of gas and failure to continue executing your contract.

15. What is a constant function in Solidity?

A constant function is one that does not make any modifications to the state of the contract. Therefore, you can call the function from anywhere without worrying about security concerns.

16. What is the concept of storage variables in Solidity?

The variables stored on the blockchain are referred to as storage variables in Solidity. These variables are used for storing important data concerning the contract. Storage variables cannot be changed and are permanent.

17. What is the first thing that needs to be defined when creating a Solidity file?

The first you should define when creating a Solidity file is the class. This helps avoid errors related to compilation that is caused due to incompatibility between various versions of Solidity. Therefore, the version number must be declared.

18. What is a smart contract’s ABI?

A smart contract’s ABI specifies its interface and the set of functions accessed from outside the smart contract. The ABI is used only for defining the events of the contract and function signatures, such as names of the function, return types, and argument types. However, it does not define their implementation.

19. What type of language is Solidity?

Solidity, which is designed for creating smart contracts, is a statically-typed programming language. It makes use of ECMAScript-like syntax. Therefore, existing web developers would be familiar with it.

20. What are the two APIs that a smart contract uses to interface with it?

The two APIs used by a smart contract to interface with it are eth_sendTransaction and eth_call. Calls, when compared to gas, as a better option because gas is expensive while calls don’t cost anything. Therefore, while gas can change the blockchain, calls don’t. However, while transactions don’t return a value, that is not the case with calls.