Sort of off topic but I am guessing you put space between those two minus signs because iOS turns two consecutive minus signs into “—”; the “em dash”.
To get around that problem, first type either as you did minus space minus, or another character between. Then long press the space bar on your onscreen keyboard so it becomes the movable cursor, move back one step and erase the character you put between.
I like to use “.” as the temporary character in between because it keeps you on the symbols keyboard and is close to the dash.
Allow me to demonstrate: C--