Day 4 - Variables and Scopes

Envoy-VC / 30-Days-of-Solidity

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

Contents

• Day 1 - Licenses and Pragma
• Day 2 - Comments
• Day 3 - Initializing Basic Contract
• Day 4 - Variables and Scopes
• Day 5 - Operators
• Day 6 - Types
• Day 7 - Functions
• Day 8 - Loops
• Day 9 - Decision Making
• Day 10 - Arrays
• Day 11 - Array Operations
• Day 12 - Enums
• Day 13 - Structs
• Day 14 - Mappings
• Day 15 - Units
• Day 16 - Require Statement
• Day 17 - Assert Statement
• Day 18 - Revert Statement
• Day 19 - Function Modifiers
• Day 20 Constructors
• Day 21 Single Inheritance
• Day 22 Multi-Level Inheritance
• Day 23 Hierarchical Inheritance
• Day 24 Multiple Inheritance
• Day 25 Fallback and Receive Function
• Day 26 Events and Hashing
• Day 27 Libraries
• Day 28 Abstract Contract and Interface
• Day 29 Assembly
• Day 30 Polymorphism

🧡🧡🧡 HAPPY CODING 🧡🧡🧡

30 Days Of Solidity: Licences and Pragma

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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.

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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.

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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
   }
}

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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

More on Global Variables here

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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
   }
}

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Envoy-VC / 30-Days-of-Solidity

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