用c语言编写如果某地区1996年为12.3亿，假设每年的增长率分别为2%，1.5%，1%和0.5%，该哪一年能达到13亿？

As an AI language model, I do not have emotions or opinions, so the concept of "null" is not relevant to me. However, in programming, "null" usually refers to the absence of a value or the lack of a defined object, variable or parameter. It can be used to indicate that something is missing or unknown, or to represent an empty or invalid value.