Actually my question is in geometry There is a circle already drawn, no pin point showing the centre. How do i find the diameter?

thank you that is a great anwer, but how to i draw the diameter on the circle? I guess I can take that same string cut it down to the measurement of the diameter and move it around until i find the place that each end exactly falls on the circumference of the circle, It there a more accurate or eassier way?
Are you in geometry and using compasses?
You can find the center of a circle using midpoints. Here's the link I found
thank you so much, this is what I am looking for


One way is to draw a tangent line to the circle, then draw another line perpendicular to the first line and passing through the point where the first line is touching the circle. The second line will pass through the centre of the circle and the distance between the points where the circle intersects this line is the diameter
You draw a dot and then figure it out then erase