Solidity (Blockchain/Smart Contracts) Questions and Answers for Viva

Answer-1: Solidity is a high-level, contract-oriented programming language used for implementing smart contracts on Ethereum and other blockchain platforms.

Answer-2: A smart contract is a self-executing program stored on the blockchain that automatically enforces terms and conditions when predefined criteria are met.

Answer-3: The file extension for Solidity source files is .sol.

Answer-4: The pragma directive specifies the version of the Solidity compiler to use. Example: pragma solidity ^0.8.0;.

Answer-5: Solidity supports data types like uint, int, bool, address, bytes, string, and mapping.

Answer-6: A struct is a custom data type that groups related variables under one type. Example: struct Person { string name; uint age; }.

Answer-7: A mapping is a key-value data structure used for storing data in Solidity. Example: mapping(address => uint) balances;.

Answer-8: Inheritance is implemented using the is keyword. Example: contract Child is Parent {}.

Answer-9: public functions can be called internally and externally, while external functions can only be called externally.

Answer-10: The fallback function is a special function executed when a contract receives Ether and no other function matches the call data.

Answer-11: The receive function is a payable function triggered when a contract receives Ether without any data.

Answer-12: A modifier is a function that can be used to change the behavior of other functions, often for access control or validation. Example: onlyOwner.

Answer-13: A constructor is defined using the constructor keyword and is executed only once when the contract is deployed.

Answer-14: events are used to log data on the blockchain, enabling communication between smart contracts and external systems like dApps.

Answer-15: Solidity storage types are storage (persistent), memory (temporary), and calldata (immutable function arguments).

Answer-16: view functions can read the blockchain state but not modify it, while pure functions do not interact with the blockchain state at all.

Answer-17: The payable keyword allows functions or addresses to receive Ether.

Answer-18: Gas is the computational cost required to execute a transaction or contract on the Ethereum blockchain.

Answer-19: Exceptions are handled using the require, assert, and revert statements to enforce conditions or stop execution.

Answer-20: An interface defines a contract's function signatures without implementation, enabling interaction with other contracts.

Answer-21: The msg object contains information about the current transaction, such as msg.sender and msg.value.

Answer-22: The block object provides information about the current block, such as block.timestamp and block.number.

Answer-23: The keccak256 function computes the hash of the input data, often used for hashing and data integrity checks.

Answer-24: Ether can be transferred using address.transfer, address.send, or address.call.value.

Answer-25: The selfdestruct function removes a contract from the blockchain and sends its remaining Ether to a specified address.

Answer-26: Libraries are reusable code modules that can be deployed once and linked to contracts. They do not have storage.

Answer-27: An abstract contract cannot be deployed directly and may contain unimplemented functions.

Answer-28: Arrays can be declared as fixed or dynamic. Example: uint[] dynamicArray; uint[5] fixedArray;.

Answer-29: Tokens are smart contracts that represent digital assets, often implementing standards like ERC-20 or ERC-721.

Answer-30: An enum is a user-defined data type for representing a set of named constant values. Example: enum Status { Pending, Completed }.

Answer-31: Reentrancy is a vulnerability where a malicious contract calls back into the original contract before the first call is completed.

Answer-32: Use the Checks-Effects-Interactions pattern or the ReentrancyGuard contract to prevent reentrancy attacks.

Answer-33: Variables declared as immutable are assigned once during the constructor and cannot be modified afterward.

Answer-34: delegatecall allows a contract to execute another contract's code in its context, preserving its storage and sender.

Answer-35: ERC-20 represents fungible tokens, while ERC-721 represents unique non-fungible tokens.

Answer-36: Use a smart contract that requires multiple approvals before executing a transaction, leveraging mappings and modifiers.

Answer-37: The require statement ensures that conditions are met before executing the remaining code, reverting if the condition fails.

Answer-38: Limitations include lack of floating-point numbers, gas inefficiencies, and potential vulnerabilities if not written carefully.

Answer-39: assert checks for conditions that should never fail, while require enforces user-defined conditions.

Answer-40: Use the indexed keyword in event definitions to allow filtering by the parameter. Example: event Log(address indexed user);.

Answer-41: The this keyword refers to the current contract's address.

Answer-42: Smart contracts are compiled to bytecode and deployed to the Ethereum blockchain via a transaction.

Answer-43: A virtual function is intended to be overridden in derived contracts.

Answer-44: The override keyword indicates that a derived contract is overriding a base contract's function.

Answer-45: Use interfaces or contract addresses to call functions from other contracts.

Answer-46: The memory keyword specifies a temporary location for variables used only during function execution.

Answer-47: block.timestamp returns the Unix timestamp of the current block, often used for time-based conditions.

Answer-48: Key features include automatic overflow checks, custom errors, and better type safety.

Answer-49: Optimize gas by minimizing storage writes, using efficient data structures, and reducing function complexity.

Answer-50: The EVM is the runtime environment for executing smart contracts on the Ethereum blockchain.