Int值急剧变化和分段错误

I've been trying to learn C++ lately, and I'm working on making a linked list of intervals that have no intersection, but i've been getting some really weird errors. My integers (obtained from get_bi or get_bs) give some pretty ridiculous values after I run the reuinion function the second time. Since those values lead to some unintended behaviour, I get segmentation faults. I thought that was the root of the problem, but I'm not sure how to fix them. I don't think I'm accessing pointers that point to nothing or whatever is causing that.I've been trying to learn C++ lately, and I'm w