Customize zsh’s prompt when displaying previous command exit code

Add this in the position in PS1 where you want the exit code to appear:

%(?..[%?] )

It’s a conditional expression. The part between the two dots (nothing in this case) is output if the expression before the first dot is true. The part after the second dot is output if it’s false.

For example:

PS1='%n%m %~ %(?..[%?] )%# '