Solidity Call, Callcode, Delegatecall Demo. Deploy contracts. Call functions and see how sender changes in either B, or C.

demo

pragma solidity ^0.4.24;

contract A {
    address public sender; 
    
    function dcall(B other, C child) public {
        other.dcall(child);
    }
}

contract B {
    address public sender;
    
    function cal(address other) public {
        other.call(bytes4(keccak256("set()")));
    }
    
    function ccode(address other) public {
        other.callcode(bytes4(keccak256("set()")));
    }
    
    function dcall(address other) public {
        other.delegatecall(bytes4(keccak256("set()")));
    }
}

contract C {
    address public sender;
    
    function set() public {
        sender = msg.sender;
    }
}