cout all variables

You can use this-->modify as per need

now just write debug(variable name) and create a separate debugging file to read the output

That mostly depends on what makes you feel comfortable. Printing everything provides a bunch of information at once, without having to do every step. Using a debugger can help understand the process leading to the bug and its cause.

Most people choose to print because it's just straightforward. However, some use a debugger (even with gdb in the terminal).

There are a lot of methods for finding errors inside the written code. Here are 2 main ones:

1. Using a debugger. Most of the IDEs provided at the olympiads have this tool. Most of all, I personally like the GDB. It is present in CLion, Code::Blocks, DevC++. It is not difficult to understand it, but it gives great opportunities in finding errors. I advise you to watch the following video — https://www.youtube.com/watch?v=J7L2x1ATOgk. In addition, if you experience memory leaks or a segmentation error, then I advise you to use valgrind (https://valgrind.org/docs/manual/quick-start.html) (a method not for traveling olympiads).

2. Stress testing. A very important skill if debugging doesn't help. I found a good article on the Russian Algorithmica — https://algorithmica.org/ru/stress-test, I hope Google translator can handle it. You can also use https://cfstress.com to search for cf tests, however this service requires a subscription for full use.

I strongly do not recommend using any cout << x to check what is currently in this variable. This not only clutters up your code, but also does not give a complete understanding of what is happening in the program.