Solidity Interview Questions (2024)
What is Solidity?
What is Ethereum Virtual Machine (EVM) in Solidity?
What is smart contract?
What is Fallback function in Solidity?
What is cryptographic hash function in Solidity?
What is delegate call in Solidity?
What is withdraw pattern in Solidity?
What is inheritance in Solidity?
What is constructor in Solidity?
Can a smart contract have multiple constructors in Solidity?
What is Abstract Contracts in Solidity?
Why use an abstract contract rather than an interface in Solidity?
What are the events in Solidity?
What is the purpose of events in Solidity?
What are the different functions used during Error Handling in Solidity?
What is difference between require and assert in Solidity?
Q: What is Solidity?
Ans:
On many blockchain platforms, particularly Ethereum, smart contracts can be implemented using the object-oriented programming language Solidity.
C++, Python, and JavaScript have significantly inspired the development of Solidity, which was made with the Ethereum Virtual Machine (EVM) in view. It allows inheritance, libraries, and advanced user-defined types.
Q: What is Ethereum Virtual Machine (EVM) in Solidity?
Ans:
Each full Ethereum node has the Ethereum Virtual Machine (EVM), a powerful virtual stack sandboxed and in charge of running contract bytecode. Usually, contracts are created using higher level languages like Solidity, which are then translated into EVM bytecode.
The Ethereum Virtual Machine was created to operate as a runtime environment for Ethereum-based smart contracts. The EVM is used by each and every Ethereum node to maintain blockchain agreement. Smart contracts, a snippet of code that runs on Ethereum, are made possible by Ethereum.
The EVM is skilled in preventing denial-of-service attacks allowing for uninterrupted communication.
Q: What is smart contract?
Ans:
Smart contracts are programs that run when specific conditions are met and are saved on a blockchain. They are often used to automate the implementation of an agreement so that all participants can be sure of the conclusion immediately, without the involvement of an intermediary or time lost. They can also automate a workflow by triggering the next activity when such conditions are met.
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Q: What is Fallback function in Solidity?
Ans:
A fallback function is a particular function that a contract can use. An unnamed external function with no input or output parameters is referred to as a fallback function. If none of the other functions match the expected function calls, EVM performs the contract's fallback function.
Q: What is cryptographic hash function in Solidity?
Ans:
An algorithm known as a cryptographic hash function creates enciphered text of a specific size using input data of any size. The output can be completely altered by even a small change in the input.
The cryptographic functions keccak256, sha256, ripemd160,
and ecrecover are available in
Solidity.
Q: What is delegate call in Solidity?
Ans:
A low level function equivalent to call is delegatecall. DelegateCall, as its name suggests, is a mechanism for calling a target contract's function by a caller contract. However, when the target contract executes its logic, the context is not on the user who performed the caller contract but rather on the caller contract.
Q: What is withdraw pattern in Solidity?
Ans:
The fund receiver has the burden of evidence due to the withdrawal pattern. A transaction must be sent by the fund receiver in order to withdraw and get their money. This makes it easier for smart contracts to pay receivers. This is so that the contract won't be affected if the money isn't transferred.
Q: What is inheritance in Solidity?
Ans:
A programmer can extend a contractor's attributes and properties to their derived contracts in Solidity by using inheritance. These features of the derived contract can also be changed by programmers through a procedure called overriding.
Q: What is constructor in Solidity?
Ans:
A Constructor is defined by utilizing the function keyword followed by an access modifier. It's an optional function that sets the contract's state variables. A function might be internal or external; an internal function marks the contract as abstract.
Q: Can a smart contract have multiple constructors in Solidity?
Ans:
A contract only allows for one constructor.
Q: What is Abstract Contracts in Solidity?
Ans:
An abstract contract is one that has at least one function but no implementation. This type of contract is known as a base contract. An abstract contract often includes both implemented and abstract functions.
Q: Why use an abstract contract rather than an interface in Solidity?
Ans:
Abstract contracts are especially effective for establishing patterns, such as the template method, which defines the skeleton of an algorithm in the superclass while allowing subclasses to alter specific sections of the algorithm without modifying its structure. It provides scalability, eliminates code duplication, and reduces overhead in case of multiple contacts.
Q: What are the events in Solidity?
Ans:
Events in Solidity are the same as events in any other programming language. When emitted, an event is an inheritable element of the contract that keeps the parameters passed in the transaction logs.
The event keyword in Solidity is used to define events. Events are called, and the
parameters
are then recorded in the blockchain. Events must initially be defined in the following manner in
order to be used:
//Event Declaration
event assetDeliver(address _from, address _to, uint _value);
//Emitting an event
emit assetDeliver(msg.sender, _to, _value);
Q: What is the purpose of events in Solidity?
Ans:
Events let external users know when anything significant occurs on the blockchain. Smart contracts unable to listen to any events on their own.
Even if all data on the blockchain is accessible to everyone and any actions may be seen by carefully examining the transactions, events are a shortcut used in conjunction with smart contracts to speed up the creation of external systems.
Q: What are the different functions used during Error Handling in Solidity?
Ans:
assert and require are utility functions for verifying for conditions.
They throw exceptions when conditions are not met.
- Before execution,
requireis used to check inputs and conditions. - The
assertfunction is used to detect code that should never be false. Failing assertion indicates that there is most likely a bug. revert()is used to stop execution and undo state changes.
Q: What is difference between require and assert in Solidity?
Ans:
- The primary difference between the two is that when the
assert()function returns false, it consumes all remaining gas and undoes all changes. require()function, when false, reverses all contract changes but refunds all outstanding gas fees we offered to pay.- This is the most commonly used Solidity function for debugging and error handling by developers.