One day, I asked my japanese friend how I could invite some friends to eat.
He said
"一緒に食べに行くかい?"
I know that we could also say:
行きましょうか(行こうか)?
行きませんか(行かない)?
行きますか(行くの)?
but I got interested in why he used "kai".
I'd like to know others situations that japanese people use "kai"