If you want to fix bugs, go after the most common ones first– such incredibly incompentent programmers alive today fail at these things:

They don’t initialize variables to a known state before using them, and then clear them when done.

They don’t initialize pointers to nil/null before allocation AND AFTER deallocation.

They don’t check the value of their previously initialized pointers after an allocation to see if memory actually got allocated.

They don’t range-check to make sure they don’t write past the end of an allocated memory buffer or array.

They don’t understand pointers and handles adequately, including dereferencing.

—
If you work on these, you’ll very quickly eliminate 80% of the problems in any code you have to fix.

Good luck to you.