Data Types

Solidity has several built-in data types, including:

1. Boolean: bool

2. Integer: int and uint with various bit sizes (int8, uint8, int256, etc.)

3. Address: address, which represents a 20-byte Ethereum address

4. Address payable: Defines the owner variable as an address that can receive ether. The msg.sender address is cast to this type in the constructor.

5. Fixed-point numbers: fixed and ufixed with various bit sizes (fixed8x1, ufixed32x18, etc.)

6. Bytes: bytes and byte with various sizes (bytes1, byte32, etc.)

7. String: string

8. Array: array with a fixed or dynamic size (uint[10], string[], etc.)

9. Struct: struct, which is a custom data type that groups several variables together

10. Mapping: mapping, which is a dynamic array-like data structure that maps keys to values

Data Types Example

// SPDX-License-Identifier: MIT pragma solidity ^0.8.0;

// Enum data type enum Color { Red, Green, Blue }

contract Example { // State variables uint public number; bool public isTrue; string public message; address public owner; address payable public payee; bytes32 public data; fixed256x18 public fixedNumber; Color public color;

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.0;

// Enum data type
enum Color { Red, Green, Blue }

contract Example {
    // State variables
    uint public number;
    bool public isTrue;
    string public message;
    address public owner;
    address payable public payee;
    bytes32 public data;
    fixed256x18 public fixedNumber;
    Color public color;

    // Struct data type
    struct Person {
        string name;
        uint age;
        uint[] favoriteNumbers;
    }

    // Array data type
    uint[] public numbers;

    // Mapping data type
    mapping(address => uint) public balances;

    // Constructor
    constructor(uint _number, string memory _message, address _owner) {
        number = _number;
        message = _message;
        owner = _owner;
        color = Color.Red;
    }

    // Function that uses a struct
    function addPerson(string memory _name, uint _age, uint[] memory _favoriteNumbers) public {
        Person memory newPerson = Person({name: _name, age: _age, favoriteNumbers: _favoriteNumbers});
    }

    // Function that uses an array and a mapping
    function addNumber(uint _number) public {
        numbers.push(_number);
        balances[msg.sender] += _number;
    }
}

Data Types Example 2

pragma solidity ^0.8.0;

contract ExampleContract {
    // State variables
    uint public myUint;
    string public myString = "Hello, World!";
    bool public myBool = true;
    address public myAddress = 0xAb8483F64d9C6d1EcF9b849Ae677dD3315835cb2;
    address payable public myPayableAddress = payable(0x5B38Da6a701c568545dCfcB03FcB875f56beddC4);
    bytes32 public myBytes32 = "hello";
    
    // Enum
    enum MyEnum {
        VALUE1,
        VALUE2,
        VALUE3
    }
    MyEnum public myEnum = MyEnum.VALUE1;
    
    // Struct
    struct MyStruct {
        uint id;
        string name;
    }
    MyStruct public myStruct = MyStruct({id: 1, name: "John"});
    
    // Arrays
    uint[] public myUintArray;
    string[] public myStringArray;
    bool[] public myBoolArray;
    address[] public myAddressArray;
    bytes32[] public myBytes32Array;
    MyEnum[] public myEnumArray;
    MyStruct[] public myStructArray;
    
    // Mappings
    mapping(uint => string) public myUintToStringMapping;
    mapping(address => uint) public myAddressToUintMapping;
    mapping(bytes32 => MyStruct) public myBytes32ToStructMapping;
    
    // Functions
    function setMyUint(uint _myUint) public {
        myUint = _myUint;
    }
    
    function addMyUintToArray(uint _myUint) public {
        myUintArray.push(_myUint);
    }
    
    function setMyString(string memory _myString) public {
        myString = _myString;
    }
    
    function addMyStringToArray(string memory _myString) public {
        myStringArray.push(_myString);
    }
    
    function setMyBool(bool _myBool) public {
        myBool = _myBool;
    }
    
    function addMyBoolToArray(bool _myBool) public {
        myBoolArray.push(_myBool);
    }
    
    function setMyAddress(address _myAddress) public {
        myAddress = _myAddress;
    }
    
    function addMyAddressToArray(address _myAddress) public {
        myAddressArray.push(_myAddress);
    }
    
    function setMyBytes32(bytes32 _myBytes32) public {
        myBytes32 = _myBytes32;
    }
    
    function addMyBytes32ToArray(bytes32 _myBytes32) public {
        myBytes32Array.push(_myBytes32);
    }
    
    function setMyEnum(MyEnum _myEnum) public {
        myEnum = _myEnum;
    }
    
    function addMyEnumToArray(MyEnum _myEnum) public {
        myEnumArray.push(_myEnum);
    }
    
    function setMyStruct(uint _id, string memory _name) public {
        myStruct = MyStruct({id: _id, name: _name});
    }
    
    function addMyStructToArray(uint _id, string memory _name) public {
        myStructArray.push(MyStruct({id: _id, name: _name}));
    }
    
    function setMyUintToStringMapping(uint _key, string memory _value) public {
        myUintToStringMapping[_key] = _value;
    }
}