{{{1}}}th c.
This is intended to provide a simple, effective way to format century abbreviations in st, nd, rd, th with a non-breaking space between the ordinal number and C. (for century).
{{C.|20|th}}
yields 20th c.
{{C.|20}}
yields 20th c.{{C.|21|st}}
yields 21st c.{{C.|22|nd}}
yields 22nd c.{{C.|23|rd}}
yields 23rd c.