• Data types

• Variables

• Constants

• Immutables

Data types

Mainly we have 4 types of data types in solidity language.

• boolean
• uint
• int
• address

boolean:

As we know we can specify a variable is true or false.

uint:

Its stands for unsigned integers. we can specify only a non negative integers.

uint can have a range of sizes like uint8, uint16 ... uint256
uint8 = 0 to 2**8-1. same goes with others.

int:

As we know we can specify an integer and negative numbers are allowed for int type. like uint here also we can specify a range of different sizes.

address:

address holds a 20 byte value which is the size of a ethereum address. additionally we can specify as address payable which can transfer or send fund to the address.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

contract ExampleDataType {

 bool public boo = true;
 uint public age = 27;
 int public num = -3;
 address public addr = 0x8CA434018A6d.....;

}

Variables

Variables are containers where we store some data. we have three type of variables.

• state
• local
• global

state:

State variables are declared inside a function and not stored in the blockchain.

local:

Local variables are declared outside of the function and stored in the blockchain.

global:

Global variables provides information about the blockchain.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

contract ExampleVariable {

  string public name = "jon doe"; // state variable.

  function changeName() public {
     uint pin = 500082;  // local variable
     address sender = msg.sender; // global variable
  }

}

constants

constants are variables that can not be modified. Their value is hard coded and using constants we can save gas.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

contract ExampleConstants {

   address public constant ADDR = 0xee3445e...;
   uint256 public constant MAX_NFT = 1000

}

Immutable

immutable variables are like constants. Value of immutable variables can be set inside the constructor but can not be modified afterwords.

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.9;

contract ExampleConstants {

   address public immutable MY_ADDRESS;

   constructor() {
       MY_ADDRESS = msg.sender;
   }

}

https://github.com/bibhu-padhy/learn-web3