Solidity

Two Families of Data Types

When a reference type is used inside a function, you must state its data location – storage, memory or calldata (Chapter 4).

Value Data Types

• Booleans – keyword bool; only two values: true or false. Operators: ! && || == !=.
• Signed / unsigned integers – int stores negative and positive whole numbers; uint stores only zero and positive numbers. Sizes go from 8 to 256 bits in steps of 8 (uint8, uint16 … uint256). uint is an alias of uint256 and int of int256.
• Fixed-point numbers – fixed/ufixed exist in the language but are not fully supported: they can be declared but values cannot be assigned to or from them. Decimals are therefore handled with integers (for example amounts in wei).
• Address – address holds a 20-byte Ethereum address of a user account or contract and has members such as .balance.
• Address payable – address payable is an address that can also receive Ether through .transfer() and .send(). A plain address is converted with payable(addr). (It is not limited to wallet addresses – a contract address can be payable too.)
• Fixed-size byte arrays – bytes1 to bytes32 hold exactly 1 to 32 bytes. bytes32 is commonly used for hashes.
• Enums – user-defined types with a fixed list of named constants (Chapter 11).
• Contract and function types – a variable can hold a contract type (e.g. Token t) or a function reference.
• Literals – fixed values written in code: numbers (42, 1e18), strings ("abc"), hex (hex"00ff"), Unicode (unicode"₹") and checksummed address literals.

Value Datatype and Keywords

Tip: type(uint8).max returns 255 and type(int8).min returns −128.

Reference Datatype

Example : Declaring Different Types

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.20;

contract DataTypesDemo {
    // value types
    bool    public isActive   = true;
    uint8   public smallNum   = 255;            // maximum value of uint8
    int256  public temperature = -12;
    address public owner      = msg.sender;    // 20-byte address
    bytes32 public fileHash   = keccak256("Solidity");

    // reference types
    uint[]  public marks;                       // dynamic array
    string  public courseName = "Solidity";
    mapping(address => uint) public balances;   // key => value

    function limits() public pure returns (uint8 maxU8, int8 minI8) {
        return (type(uint8).max, type(int8).min);   // (255, -128)
    }
}

Key Takeaways

The PDF E-Notes are the earlier printable version of this chapter. The notes on this page are the latest, revised version.

Video : Solidity Data Types

Resource File

• Chapter 3 : Solidity File

Question / Answer (15 questions)

MCQ Test : Check Your Understanding (5 questions)

Select an option and press Check Answer, or answer all questions and press Submit Test to see your score. Each answer comes with an explanation.

Bibliography/References

The notes, questions and MCQs on this page are original explanations written for this course. The works listed below were consulted and are cited for attribution and further reading. Product names, logos and trademarks belong to their respective owners. Short quotations, where used, are marked and attributed.

1. Solidity Team. (n.d.). Types (value types, reference types, mappings, operators, conversions). Solidity Documentation. https://docs.soliditylang.org/en/latest/types.html
2. Solidity Team. (n.d.). Cheatsheet. Solidity Documentation. https://docs.soliditylang.org/en/latest/cheatsheet.html
3. Modi, R. (2018). Solidity Programming Essentials: A beginner’s guide to build smart contracts for Ethereum and blockchain. Packt Publishing. ISBN 978-1-78883-138-3.
4. Antonopoulos, A. M., & Wood, G. (2018). Mastering Ethereum: Building Smart Contracts and DApps. O’Reilly Media.