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Vedant Chainani

Posted on Jun 1, 2022 • Edited on Jul 21, 2022

Day 4 - Variables and Scopes

#100daysofcode #solidity #web3 #blockchain

envoy1084 / 30-Days-of-Solidity

30 Days of Solidity step-by-step guide to learn Smart Contract Development.

WARNING: This repository is currently undergoing updates and revisions to incorporate the latest information and advancements in Solidity programming. Please be advised that the content may not be up-to-date or accurate during this time. We expect the updates to be completed within the next 30 days, and appreciate your patience during this process. Thank you for your understanding.

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This is Day 4 of 30 in Solidity Series
Today I Learned About Variables and Scopes in Solidity.

Variables

Solidity supports three types of variables.

State Variables − Variables whose values are permanently stored in a contract storage.
Local Variables − Variables whose values are present till function is executing.
Global Variables − Special variables exists in the global namespace used to get information about the blockchain.

While naming your variables in Solidity, keep the following rules in mind.

You should not use any of the Solidity reserved keywords as a variable name. For example, break or boolean variable names are not valid.
Solidity variable names should not start with a numeral (0-9). They must begin with a letter or an underscore character. For example, 123test is an invalid variable name but _123test is a valid one.
Solidity variable names are case-sensitive. For example, Name and name are two different variables.

State Variable

Variables whose values are permanently stored in a contract storage.

pragma solidity ^0.8.6;

contract SolidityTest {
   uint storedData;      // State variable
   constructor() public {
      storedData = 10;   // Using State variable
   }
}

Local Variable

Variables whose values are available only within a function where it is defined. Function parameters are always local to that function.

pragma solidity ^0.8.6;
contract SolidityTest {
   uint storedData; // State variable
   constructor() public {
      StoredData = 10;
   }
   function getResult() public view returns(uint){
      uint a = 1; // local variable
      uint b = 2;
      uint Result = a + b;
      return Result; //access the local variable
   }
}

Global Variables

These are special variables which exist in global workspace and provide information about the blockchain and transaction properties.

Name	Returns
blockhash(uint blockNumber) returns (bytes32)	Hash of the given block - only works for 256 most recent, excluding current, blocks
block.coinbase (address payable)	Current block miner's address
block.difficulty (uint)	Current block difficulty
block.gaslimit (uint)	Current block gaslimit

Variable Scopes

Scope of local variables is limited to function in which they are defined but State variables can have three types of scopes.

Public − Public state variables can be accessed internally as well as via messages. For a public state variable, an automatic getter function is generated.
Internal − Internal state variables can be accessed only internally from the current contract or contract deriving from it without using this.
Private − Private state variables can be accessed only internally from the current contract they are defined not in the derived contract from it.

eg-

pragma solidity ^0.8.6;
contract C {
   uint public data = 30;
   uint internal iData= 10;

   function x() public returns (uint) {
      data = 3; // internal access
      return data;
   }
}
contract Caller {
   C c = new C();
   function f() public view returns (uint) {
      return c.data(); //external access
   }
}
contract D is C {
   function y() public returns (uint) {
      iData = 3; // internal access
      return iData;
   }
   function getResult() public view returns(uint){
      uint a = 1; // local variable
      uint b = 2;
      uint result = a + b;
      return storedData; //access the state variable
   }
}

envoy1084 / 30-Days-of-Solidity

30 Days of Solidity step-by-step guide to learn Smart Contract Development.

WARNING: This repository is currently undergoing updates and revisions to incorporate the latest information and advancements in Solidity programming. Please be advised that the content may not be up-to-date or accurate during this time. We expect the updates to be completed within the next 30 days, and appreciate your patience during this process. Thank you for your understanding.