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This topic is about Solidity – Variable Scope.

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.

Example

pragma solidity ^0.5.0;
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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