Why is it better to pass data through function parameters instead of working with them globally?

Question

Programming

I have a C exam tomorrow, and I still can't think of a clear answer to the question why is it better to pass data to a function through parameters than to work with them through the global scope? Thanks in advance.

Answer 1

Because the use of parameters ensures the purity of functions, and therefore increases the modularity of the program, reusability, and in some cases even parallelization.