Printing an geomterical object/structure and determining the mid point of the two lines passing through it

I am very basic in C programming, may be printing a variable or so.

Can any one of you can help me to give me a example code or guide me how to construct an object and determine its mid point? Or to be more precise. Let us assume I have an object and I want to print that object point by point (e.g. a sphere or square or rectangle) and two lines are passing through it, which would help me to determine the mid point of that object.

Sorry if my explanation is confusing. Thanks in advance. I really want to take this the next level. But this is my first step and despite trying for for several weeks I am unable to do so. Please help me.

[Example Rough Image]