30+ Solidity Interview Questions And Answers
Solidity is a programming language designed for developing smart contracts that run on the Ethereum blockchain. It is statically typed, supports inheritance, libraries, and complex user-defined types among other features. Solidity is used to create contracts for voting, crowdfunding, blind auctions, and multi-signature wallets. When interviewing for a Solidity developer, questions can range from basic syntax knowledge to complex contract deployment scenarios.
Most asked Solidity interview questions
Beginners
1.
What is Solidity?
1.
What is Solidity?
Solidity is a contract-oriented, high-level programming language for implementing smart contracts on various blockchain platforms, primarily Ethereum.
2.
Can you explain what a smart contract is?
2.
Can you explain what a smart contract is?
A smart contract is a self-executing contract with the terms of the agreement between buyer and seller being directly written into lines of code. The code and the agreements contained therein exist across a distributed, decentralized blockchain network.
3.
What is a contract in Solidity?
3.
What is a contract in Solidity?
In Solidity, a contract is a collection of code (its functions) and data (its state) that resides at a specific address on the Ethereum blockchain.
4.
Explain the use of the 'function' keyword in Solidity.
4.
Explain the use of the 'function' keyword in Solidity.
Function is a fundamental block of Solidity and is used to define what actions the contract can perform.
5.
What does the 'public' keyword indicate in a function?
5.
What does the 'public' keyword indicate in a function?
The 'public' keyword makes a function callable from outside the contract. Without this keyword, other contracts have no way to access the function.
6.
How does the 'view' function modifier work with functions?
6.
How does the 'view' function modifier work with functions?
A 'view' function declares that no state will be changed. This means the function is only viewing the data but not modifying it.
7.
What is an event in Solidity?
7.
What is an event in Solidity?
An event is an inheritable member of the contract which is used to log transactions to the Ethereum blockchain. It helps in external listening.
8.
Guess what this Solidity code does:
function getBalance() public view returns (uint) {
return address(this).balance;
}
8.
Guess what this Solidity code does:
function getBalance() public view returns (uint) {
return address(this).balance;
}This function returns the balance of Ether stored in the contract.
9.
Define 'modifier' in Solidity.
9.
Define 'modifier' in Solidity.
A modifier is used to change the behavior of a function in a declarative way.
10.
Explain 'msg.sender'.
10.
Explain 'msg.sender'.
msg.sender is a predefined variable that refers to the address of the person (or contract) who called the current function.
11.
What is the purpose of 'require' in Solidity?
11.
What is the purpose of 'require' in Solidity?
'require' is used to ensure that certain conditions are met. If the condition is not met, the operation is reverted.
12.
How are Ethereum addresses formatted?
12.
How are Ethereum addresses formatted?
Ethereum addresses are typically presented as 42-character hexadecimal strings prefixed with '0x'.
13.
What does the 'payable' keyword allow?
13.
What does the 'payable' keyword allow?
The 'payable' keyword allows a function to receive Ether while it's being called.
14.
Can Solidity functions accept multiple parameters?
14.
Can Solidity functions accept multiple parameters?
Yes, Solidity functions can accept multiple parameters separated by commas.
15.
Describe the process of creating a new contract from another contract in Solidity.
15.
Describe the process of creating a new contract from another contract in Solidity.
This can be achieved by using the new keyword followed by the contract name with parameters, if any are needed for the constructor.
Advanced
1.
What are gas and gas limit in Ethereum?
1.
What are gas and gas limit in Ethereum?
Gas is a measure of the computational work required to do a certain operation, while gas limit is the maximum amount of gas that can be used in each block.
2.
Explain how inheritance works in Solidity.
2.
Explain how inheritance works in Solidity.
Solidity supports single and multiple inheritance. Contracts can inherit other contract functions and properties.
3.
What's the difference between 'memory' and 'storage' keywords?
3.
What's the difference between 'memory' and 'storage' keywords?
'Memory' stores temporary variables, and 'Storage' holds permanent variables that persist between function calls.
4.
Define 'internal' and 'external' visibility modifiers.
4.
Define 'internal' and 'external' visibility modifiers.
Internal functions are those that are only accessible from the contract itself and its derived contracts. External functions can only be called from outside the contract.
5.
What's the use of the 'interface' contract in Solidity?
5.
What's the use of the 'interface' contract in Solidity?
An 'interface' facilitates the declaration of functions that can interact with other contracts and is intended for external use.
6.
Describe the SHA-3 and KECCAK256 hash functions.
6.
Describe the SHA-3 and KECCAK256 hash functions.
Both are cryptographic functions used in Ethereum for security purposes, often for hash operations in smart contracts.
7.
What does Solidity's 'mapping' allow you to do?
7.
What does Solidity's 'mapping' allow you to do?
Mapping provides a way of storing structured data within smart contracts.
8.
Describe how Solidity handles array types.
8.
Describe how Solidity handles array types.
Solidity provides both dynamic and fixed-sized array types. Arrays can contain any type, including structs.
9.
What are state modifiers?
9.
What are state modifiers?
State modifiers are keywords like public, internal, private, and external that define variable accessibility.
10.
Explain the significance of the fallback function in Solidity.
10.
Explain the significance of the fallback function in Solidity.
The fallback function is a default function which is called when a contract is sent Ether with no other data.
11.
Detail how custom errors can be defined and used in Solidity.
11.
Detail how custom errors can be defined and used in Solidity.
Custom errors provide a way to return more detailed error information and can be cheaper than 'require' statements.
12.
Explain state mutability keywords in Solidity.
12.
Explain state mutability keywords in Solidity.
State mutability keywords like pure, view, and payable declare the nature of state change in a function.
13.
How are contract upgrades handled given that Ethereum contracts are immutable?
13.
How are contract upgrades handled given that Ethereum contracts are immutable?
Upgradeability can be achieved using proxies and other design patterns like the factory pattern.
14.
What are libraries in Solidity?
14.
What are libraries in Solidity?
Libraries are reusable pieces of code that a contract can call, but cannot declare state variables.
15.
Give an example of a Solidity code that demonstrates a loop with a break condition
15.
Give an example of a Solidity code that demonstrates a loop with a break condition
Here is a simplified loop that breaks when a specific condition is met:
for(uint i = 0; i < 10; i++) {
if(i == 5) {
break;
}
}Solidity Interview Tips
Maintain Composure
-
It's essential to stay calm during the interview, particularly when faced with tough questions. Take your time to understand the question and gather your thoughts. Breathing exercises prior to entering the interview can help manage anxiety and promote clearer thinking.
Structured Responses
-
Use a structured approach like the STAR method (Situation, Task, Action, Result) to answer questions. This method can help articulate your responses clearly, providing a logical flow and making your answers more comprehensive and digestible for the interviewer.
Understanding the Question
-
Ensure you clearly understand the question asked. Don't hesitate to ask for a clarification or ask the interviewer to repeat the question. This shows that you pay attention to details and are invested in providing the correct answer.
Practical Examples
-
When discussing technical concepts or previous job experiences, provide practical examples that showcase your understanding and skills. This will make your answers more engaging and credible. Prepare a few case studies or projects in advance that demonstrate your expertise and problem-solving skills.
Continuous Learning
-
Expressing a willingness to learn and adapt is crucial, especially in tech fields like Solidity development, where continuous updates and learning are part of the job. Highlighting your commitment to professional growth can significantly impress your interviewer and increase your chances of securing the job.
FAQs
How much does it cost to hire a Solidity developer?
The cost to hire a Solidity developer can vary depending on their level of experience and the complexity of the project. Typically, it starts at $45 per hour at FireHire. We provide flexible engagement models to fit different budgetary requirements. Read more
How much do Solidity developers charge?
Solidity developers' charges are largely dependent on their expertise, the project's duration, and specific needs. On average, rates start from $45/hour at FireHire, ensuring you get expert developers at competitive rates. Read more
How do I find a Solidity developer?
Finding a Solidity developer is easy with FireHire. Our platform hosts a vast network of over 1600 pre-vetted developers, allowing you to quickly find the right talent with the right expertise. Just reach out to us, and we'll connect you with suitable candidates in just five days. Read more
Why using FireHire for hiring Solidity developers is the best choice?
Choosing FireHire for hiring Solidity developers ensures you get quality, efficiently. With our seasoned, pre-vetted developers, risk-free hiring with a 30-day replacement guarantee, and a quick candidate delivery time averaging 5 days, we stand out as the prime choice for your development needs.
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