example.sol

pragma solidity 0.5.4;
contract helloWorld {
    string data;
    function pureHelloWorld() public pure returns(string memory) {
        return "hello world";
    }
    function readStrData() external view returns(string memory) {
        return data;
    }
    function sendStrData(string memory sendData) public {
        data = sendData;
    }
}