[Solidity] Summary of data types

This section provides a summary of data types in Solidity.

List of Solidity data types

The table below lists the Solidity data types.

Data Type	Possible Value	Default Value	Remarks
bool	Boolean (true/false)	false	-
int	Signed integer (-2 n-1 to 2 n-1 - 1)	0	Exists from int8 to int256 and 8 bits each. int is alias with int256.
uint	Unsigned integer (0 to 2 ** n - 1)	0	Exists from uint8 to uint256 and 8 bits each. uint is alias with uint256.
fixed	Signed fixed-point number	0	Exists from fixed8 to fixed256 and 8 bits each. fixed is alias with fixed256.
ufixed	Unsigned fixed-point number	0	Exists from ufixed8 to ufixed256 and 8 bits each. ufixed is alias with ufixed256.
address	Ethereum Address	address(0)（0x0000000000000000000000000000000000000000）	-
bytes	Byte array	0x	-
string	String	"" (empty string)	-
enum	Enumerative type	First element in an enumerated type.	Enumerate constants (values are assigned sequentially with the first element as 0).
struct	Structure	-	Combine variables of different data types into a single type.
mapping	Mapping - Key/Value Pairs	Depends on the data type of the mapping value.	-
array	Array	[] (empty array)	Two types of arrays exist: fixed-length and variable-length.

List of data types (Solidity)

Sample Code

// SPDX-License-Identifier: GPL-3.0

pragma solidity >=0.7.0 <0.9.0;

contract Test {

    /* bool (boolean) */
    bool varBool = true;
    
    /* int (signed integer) */
    int varInt = -1;
    int varInt8 = 1;
    int varInt16 = -1;
    int varInt32 = 1;
    int varInt64 = -1;
    int varInt128 = 1;

    /* uint (unsigned integer) */
    uint varUint = 1;
    uint varUint8 = 1;
    uint varUint16 = 1;
    uint varUint32 = 1;
    uint varUint64 = 1;
    uint varUint128 = 1;

    /* fixed (signed fixed-point number) */
    fixed varFixed = -0.1;
    fixed varFixed8 = 0.1;
    fixed varFixed16 = -0.1;
    fixed varFixed32 = 0.1;
    fixed varFixed64 = -0.1;
    fixed varFixed128 = 0.1;

    /* ufixed (unsigned fixed-point number) */
    ufixed varUfixed = 0.1;
    ufixed varUfixed8 = 0.1;
    ufixed varUfixed16 = 0.1;
    ufixed varUfixed32 = 0.1;
    ufixed varUfixed64 = 0.1;
    ufixed varUfixed128 = 0.1;

    /* address (Ethereum address) */
    address varAddress = 0x0000000000000000000000000000000000000000;
    
    /* bytes (byte array) */
    bytes varBytes = "0x0";
    bytes1 varBytes1 = "0";
    bytes32 varBytes32 = "0x1234567890";

    /* string */
    string varString = "hello";

    /* enum (enumerated type) */
    enum Colors {
        Red,   // 0
        Green, // 1
        blue   // 2
    }

    /* struct (structure) */
    struct User {
        uint id;
        string name;
        address balance;
    }

    /* mapping (mapping - key/value pairs) */
    mapping (address => uint) balances;

    /* array */
    // fixed-length array
    string[2] members = ["bob", "alice"];
    // variable-length array
    uint[] numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10];

}

Each data type has a different cost (gas cost). When creating more sophisticated applications, it is important to understand the cost of each data type.