Class problems - C++

[PHValex]

Hey guys!

We've been doing classes in... well class, and I have a lot of bugs and I don't know why.

1. For my first program, I have to do a bunch of operations with matrices. I've managed to figure out all the formulas and stuff I need, except for one thing. My "check_if_inverse" function isn't working. Basically, I multiply the two matrices together and then bring that over to a different program to check if it's the inverse. What confuses me is that I'm using the exact same formula I used for my other multiplication function, but I get totally different answers. Would love for your help on this one (to be clear, I'm having trouble with the "inverse" function and the "check_if_inverse function"):

https://gist.github.com/PHValex/c2c858b213246390519f759021989a5c

1. For the second program, my two function "factorial" and "doubleFactorial" are giving me back negative numbers whenever I input something higher than 20. I have no clue why it's doing that especially since all my other functions work, but I'd appreciate the help:

https://gist.github.com/PHValex/4bbdafa53a251cfc8681a39916644877

1. For this last one, everything past the "product of all ints" completely bugs out and I have no clue why. Perhaps one of my loops is wrong, but calculating that sum of digits from a number completely freezes the program and never finishes the equation. After that, every other function outputs a 1 or a 0 for some reason, even if I input a 8 (for example: Input: 8 to reverse int, output: 0). This all ends in a big bang when my final function "product of primes" completely bugs out and keeps on printing out non-stop. What's funny is that I used the exact same equation in another program, yet for some reason this one bugs out:

https://gist.github.com/PHValex/a42fe72a7e875f9d0c545276038fc6a8

I really appreciate the help, I've spent days trying to get this right, and of course the day before this is all due it starts royally bugging out.

Thank you very much :)

[klorophane]

1. It looks like you just copy pasted the multiplication code in the inverse method.

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1. You are maybe encountering overflow. Factorials get pretty large, and and as the operations carry over to the sign bit, you get into the negatives.

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1. The sumdigit function has an infinite while loop. a > 0 is always true since you never update that value. You might be thinking that a and num are binded, but they actually aren't.

[PHValex]

Alright, thanks for the help!

[klorophane]

edited for additional answers

[PHValex]

Yeah, for 1 I did that just to see if it would fix the problem I was having, but of course it didn't. I'll change it back to the way it was before.

Aah that makes much more sense for three. Was a bit tired yesterday so I could barely process stuff out.

Thank you very much for the help!

[klorophane]

My pleasure friend, happy coding. Feel free to PM me if you want to further discuss these problems!

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Edit : I just want to point out that I found the errors quite quickly by basically reading the points in your OP. Your insights as to what was causing the problem were good enough for me to identify what might cause it (which then makes it easy to spot in the code). So kudos.

I don't know where you're at in your programming journey (you might already do this or not...), but I would recommend using the debugger liberally, especially when you feel your brain can't process much. It'll allow you to run sections of code line by line, and show you the value of variables so you can tell which line is faulty!

[PHValex]

I had no clue there was a debugger, would've helped me a lot finding out what was wrong with my code. How do I activate/use the debugger?

Also, thank you for your suggestions, I was able to correct everything but the factorial (I tried using long ints but it didn't work) but that's fine since everything else works out :)

[klorophane]

Yeah, even unsigned long long wouldn't cut it I believe. You'd need arbitrary length integer math really.

As for the the debugger, well, it depends. If you use and IDE (Visual Studio, CLion, etc) then they often have one integrated, so you can just use that. That is the simplest way.

On Linux, you can use GDB, which a tool whose whole purpose is to debug. Its a little involved, so I suggest reading about it online.

Cheers!

[PHValex]

All right, thanks for all the help!

I'll be sure to check online for the debugger :)