remove all line segments

C# Code!

[CgsAddInMacro]
public void RemoveLineSegment()
{
    Curve c = corelApp.CreateCurve();
    Shape s = corelApp.ActiveShape;
    s.ConvertToCurves();
    Segments segs = s.Curve.Segments;
    for (int i = 1; i <= segs.Count; i++)
    {
        if(!segs[i].Type.Equals(cdrSegmentType.cdrLineSegment))
        {
            c.AppendCurve(segs[i].GetCopy());
        }
    }
    s.Curve.CopyAssign(c);
}

This is the basis for what you are looking for, understand what the code does and write your project with your needs.