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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
30 Days Of Solidity: Licences and Pragma
Author …
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 |
More on Global Variables here
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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