Also, from Remix "Contracts" tab, I successfully sent "setGreeting" and "greet" messages to my contract, by clicking a button.
Now, I want to let a friend use the same contract using the same convenient GUI of Remix. To see how it works, I opened Remix in an incognito window. I went to the "Contracts" tab.
EDIT: I clicked the button named "At Address" and entered the address of my contract, but got this error:
Apparently, Remix opens with the default contract ("ballot") and tries to find the "winningProposal" of my contract. But, my contract does not have this field since it is a different contract ("Hello")!
Does it mean that I have to send my friend the entire source-code of my contract, to put in Remix?
Is there another way to easily let my friend play with my contract?