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Top 25 Solidity Interview Questions with Answers

Mihaela Popa

21 Dec 2022

6 min read

Top 25 Solidity Interview Questions with Answers
  • Solidity

Interviews can be intimidating, but they don’t have to be! You just need to know what you’re walking into—and that’s where this list of the top Solidity interview questions comes in! Solidity is an object-oriented programming language for writing smart contracts on Ethereum Virtual Machine (EVM), which supports various types of test cases and assertions, such as unit testing and property testing, to improve code quality and make it easier to identify bugs in the smart contracts being developed by programmers. This can be extremely important when dealing with large sums of money, so knowing how to write smart contracts that work correctly and have fewer bugs is essential in the field of blockchain development.

Learn what employers will ask you so you're prepared with answers that will impress them and help you land the job you want! Whether you are looking for blockchain developer jobs or interviewing for your own career advancement, the following Solidity interview questions are among the most common ones.

In what sense is solidity defined?

Smart contracts are implemented on Ethereum using Solidity. By compiling to bytecode, the program can be executed by the Ethereum Virtual Machine (EVM). The language was developed by Gavin Wood, Christian Reitwiessner, Alex Beregszaszi, Liana Husikyan, and others as part of the ETH project.

What is a smart contract's ABI?

A Smart Contract's ABI is an interface for humans to interact with the contract. It is a JSON-based document that describes the functions, events, types, and other ABIs of that contract. It serves as documentation for developers and users who want to interact with it.

What is EVM bytecode?

EVM bytecode is the bytecode that is executed by the Ethereum virtual machine (EVM). It's a low-level bytecode, meaning that it doesn't have an abstract syntax tree and instead operates on individual bytes. The instructions are designed to be easy for a computer to execute because they use simple instructions such as adding two numbers together or looking up a word in memory.

What are the benefits of using smart contracts on Ethereum?

The benefits of using smart contracts on Ethereum are that they are fast, cheap, and immutable. Smart contracts can be used to create a wide variety of applications on the Ethereum blockchains, such as a lottery, an escrow system, or an automatic payment system. But before you start coding your first smart contract on Ethereum, let's go over some important concepts.

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

In computing, enum stores named constants. They are usually used to store different types of values, such as short, long, or float. Enums have restrictions on their use because they cannot be changed to store other types of values.

What is a library and how many types are there?

A library is a collection of code that is shared among many projects. There are many types of libraries, including open-source, private, and public. Open-source libraries can be used by anyone, as long as they follow the licensing agreement. Private libraries are only available to the owner's team or company. Public libraries make their code available for anyone to use and change as they please.

What is the consensus algorithm’s function?

Different consensus algorithms have different functions. Proof of work is a type of consensus algorithm that is most commonly used by blockchains. It ensures that transactions are verified, and it rewards the miners for maintaining the blockchain. Proof of stake is a different type of consensus algorithm, which makes use of delegate nodes to verify transactions.

Is Solidity the future?

Solidity is a programming language for writing smart contracts, which are programs that can be deployed on the Ethereum blockchain. In order to write a smart contract, you need to learn how to code using solidity and then compile it into an Ethereum-readable format. In the future, if more industries adopt this technology, we might see a rise in more jobs related to writing solidity smart contracts such as software engineers.

What type of language is Solidity?

Solidity is a high-level language whose syntax is similar to that of JavaScript and it runs on the Ethereum Virtual Machine.

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

The first thing that needs to be defined when creating a Solidity file is the pragma. The pragma is used to specify the compiler version and the source language of your code, as well as some other options. For example, if you are compiling a smart contract written in C++, you would use pragma solidity ^0.4.23; to specify that your code is written in C++ and compiled by the newer version of Solidity compiler (solidity 0.4.23).

How do you create an instance of a contract class in Solidity?

A contract instance is created by calling the constructor function. In order to create a new contract, one should first create a new class for it. The following are the steps to creating an instance of a contract class:

1) Define the contract's class and implement its functions, including any necessary state variables. 2) Create a constructor and initialize all state variables as public properties in the constructor code. 3) Add a destructor that clears out the state variable data. 4) Add getter and setter methods for each variable so they can be accessed externally.

What types of applications can be developed using Solidity?

Solidity is a programming language that is used to build applications on the Ethereum Virtual Machine. With the use of Solidity, it is possible to create smart contracts and Dapps. It can also be applied to games like CryptoKitties.

What’s the difference between a wallet address and an account in Ethereum?

A wallet address is a public/private key pair that is used to send or receive Ether from one address to another. Accounts are created by wallets and store Ether balances. There are two types of accounts: externally owned accounts (EOAs) and contract-based accounts.

Can you explain the concept of storage variables in Solidity?

Solidity has two types of storage variables: state variables and local variables. State variables are globally accessible from within the smart contract, while local variables exist only within the body of a function and cannot be accessed outside of it.

What is a constant function in Solidity?

A constant function is a function that takes no parameters and always returns the same value. It can be called at any point in the program, regardless of how many times it has been called before.

What is the difference between require and assert in Solidity?

Require is used to make sure a condition is true while assert is used to check that the result of an operation is what it should be, and throw an error if it's not.

What are the events in Solidity?

Events are a specific type of function, different from regular functions because they can only be triggered by external sources, such as the blockchain or another contract.

What are the advantages of using Solidity over other similar programming languages?

With its syntax being similar to JavaScript, Solidity is a contract-oriented, high-level language designed to target the Ethereum Virtual Machine. One of the most important benefits that Solidity has over other programming languages is its tight integration with the Ethereum Virtual Machine (EVM) and ability to compile down to the bytecode that runs on it.

How can you protect yourself from a re-entry attack?

You can protect yourself from a re-entry attack by splitting the private key into two different pieces and storing them in different locations. One piece is used to sign transactions, while the other is only used to create new addresses.

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

The two APIs that a smart contract uses to interface with it are the Ethereum Virtual Machine (EVM) and the Solidity programming language.

What is Truffle?

This is a toolkit for developing and testing Ethereum assets. It provides a set of libraries to interact with the blockchain so you can develop applications that utilize smart contracts.

Give some details on the Truffle development environment: framework, structure, and migrations.

Ethereum smart contracts can be developed, tested, and deployed using this framework. Truffle was created by ConsenSys and provides tools for developers to build DApps.

Why Truffle is recommended while working with Solidity?

Truffle is an open-source development environment, testing framework, and asset pipeline for Ethereum. It provides a set of tools to build and run distributed applications that work on top of the Ethereum blockchain.

What is the withdrawal pattern in Solidity?

The withdrawal pattern is a process that runs when the user requests to withdraw from their account. The first thing the program checks for is whether or not the withdrawal amount is greater than or equal to the current balance.

What is a cryptographic hash function in Solidity?

A cryptographic hash function is a mathematical algorithm that takes an input and converts it into a fixed-size string, called a hash.


In conclusion, we have come up with a list of the top 25 solidity interview questions. We hope that this list will help you ace the interview and land your dream job as a smart contract developer. Thank you for reading this blog post! If you liked it, please share it with others who might be interested.

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Mihaela Popa

Marketing Manager at WorksHub

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