React router V4 doesn't works - reactjs

Question

Since 3 days i am working on react route but its not working..I
I dont know where i am doing wrong even simple route is not working...if simple routing(without params) work then i wanted to pass ID to the NEW component..
But i am able to pass ID optionally ..IF i remove ? then routing doesnt works.. I have tried using switch and exact too..
And One More issue is by passing ID optionally i am getting Undefined in New Component Page During render (First time)..So i wanted to pass ID:1 from router .Please help me out...Thanks
<Route name="ideas" path="/Hello" component={New} /> (Not Working)
<Route name="ideas" path="/:Hello" component={New} /> (Not working)
<Route name="ideas" path="/New/:Hello?" component={New} />(Not working)
<Route name="ideas" path="/" component={New} /> {Working}
<Route name="ideas" path="/:Hello?" component={New} /> (working)
import React from 'react';
import ReactDOM from'react-dom'
import New from './New'
import Demo from "./demo";
import {
BrowserRouter as Router,
Route,
Switch,
} from 'react-router-dom'
function App() {
return (
<div>
<Router>
<Route name="ideas" path="/Hello" component={New} />
</Router>
</div>
);
}
ReactDOM.render(
<App />,
document.getElementById("root")
);
export default App;

Answer 1

I updated your codesandbox. You were not using Switch from react-router-dom. Which is necessary when dealing wit routes. Please check updated codesandbox.
Use it in following way
import React from "react";
import ReactDOM from "react-dom";
import New from "./New";
import { BrowserRouter as Router, Route, Switch } from "react-router-dom";
function App() {
return (
<div>
<Router>
<Switch>
<Route name="ideas" path="/Hello" component={New} />
</Switch>
</Router>
</div>
);
}
ReactDOM.render(<App />, document.getElementById("root"));
You can also have a look at https://codesandbox.io/s/smoosh-currying-8job8.
Updated version of your code:
https://codesandbox.io/s/unruffled-hellman-2f19h