[slowglass]

You can also do

pattern = "I have sold <<1[no items/a single item/$d items]>>."
msg = zo_strformat(pattern, num)

If num = 0
msg = "I have sold no items"

if num = 1
msg = "I have sold a single item"

if num > 1 (ie 5 in this case)
msg = "I have sold 5 items"