easy but it doesn't work ... in react the if / else in this example

What am I missing to make it work? I suppose the answer is very easy, but really, I'm starting in React and still do not know why it does not work. If anyone knows, I am very grateful.

Thanks.

import React from 'react';

var a=30;
var b=20;

function App() {
  return (
    <div>
    <h1>if or else</h1>
    <c/>
    </div>
  );
}

export default App;

function c(a,b) {
  if (a >= b){ 
  return (
    <div> 
    <h2> A is greater than B</h2>
    </div>
    );
 }
  else {
     return (
      <div> 
       <h2>B is greater than A</h2>
      </div>
    );
 }
}