8051 C complier

Jon,

I understand the first part of the code, but I'm not sure about the second part where P1 = (x % 10) | (((x / 10) % 10) << 4);

Would you mind explain it to me?

Andrew,

Yes, I figured I couldn't use ACC directly; I used it to trial-and-error.

Jon,

I understand the first part of the code, but I'm not sure about the second part where P1 = (x % 10) | (((x / 10) % 10) << 4);

Would you mind explain it to me?

Andrew,

Yes, I figured I couldn't use ACC directly; I used it to trial-and-error.

I'm not sure about the second part where P1 = (x % 10) | (((x / 10) % 10) << 4);

That's the part that's actually C code. If you don't understand that, it's time to break out a C text book and learn about the C programming language. If you don't understand that, you don't know C. It seems that's what several other posters have been trying to tell you.

Jon

I know, I never denied I don't need to learn C, I also didn't say I'm a pro at C. Hence I'm here to ask for help. If I knew the answers to my questions are "you don't know C, learn it", then I would probably just went straight there to begin with, and answer the questions myself sooner or later. Don't get me wrong, I'm not saying all these replies are not helpful, it really strike me hard to make myself think how little do I know about C versus embedded. Although I would be much more appreciated if anyone could give me a hand and guide me to the right direction while pointing out my problems, than just pointing out my problems without additional help to correct my problem.

I really appreciated your example code, I will run your code and see what happens while I will learn C to stop embarrassing myself.

Thanks.

"I would be much more appreciated if anyone could give me a hand and guide me to the right direction while pointing out my problems"

But your fundamental problem is precisely that you need to spend time learning the 'C' language!

That is absolutely fundamental. We cannot build anything further until you have laid that foundation.

You've just shown that yourself: Jon gave you some 'C' code, but you couldn't uderstand it - because you haven't got that basic foundation to enable you to understand 'C' code!

First step.

Learn the operators.

Then you would know that x % 10 would perform a modulo operation, and extract the least significant decimal value from a number. And you would know that x / 10 would perform (in this case) an integer divide, and throw away the least significant decimal digit - which (if your number is strictly within the 0..99 range) would extract the most significant decimal digit.

And combining the above knowledge, you would then understand that ((x / 10) % 10) would support numbers larger than 99, and extract the second least significant digit, so if you had the number 12345 (given that x has a data type that can store this, i.e. a 16-bit or larger type and not an 8-bit type) it would first cut away the digit (5) giving 1234 and then extract that last decimal digit (4).

And you would then also know the meaning of << and understand that (expr) << 4 would multiply that value by 16 by moving the value four steps to the left in the variable, leaving the four lowest bits zero.

And you would also know that | is a bit-and, so it will merge the bit patterns from the expression to the left, and the expression to the right.

So suddenly, you would see of the expression takes a numeric value x, splits out the two least significant decimal digits from it, and place them in the high and low nibble of the P1 port.

The code would be a bit simpler if it could assume that the number is already from the start in the 0..99 range, but as written it allows values larger than 99, by throwing away higher-valued decimal digits.

C isn't black magic. There are few operators. There are few reserved keywords. Programs are just formed by combining these few LEGO pieces into larger and larger constructs, until you get a program that performs the task at hand.

So your goal must be to learn what LEGO pieces you have access to. And then figure out how to subdivide your task into smaller pieces until each piece is small enough that you are able to convert that little subtask into individual C statements.

"I really appreciated your example code,"

andrew is absolutely right: you don't need sample code. all you need is to pick up a good C book and understand it.

at this point, giving you sample code does more harm to you.

at this point, giving you sample code does more harm to you.

I'm not sure I would go THAT far. I think most of us learned a lot of what we know about programming by examining other people's code and trying to figure out how it worked. However, I didn't learn much by asking other to tell me the answers. I worked hard to figure things out for myself.

The example code I gave is trivial. There's nothing tricky about it. It uses typical C operators. Now it's time for the OP to break out a C book and see what it is that % and / and << do. If he has written assembly code and taken elementary to middle school math, it won't be hard.

Jon

I found it more helpful to learn by looking at other people's code and comparing them to see which one is more efficient. But that's my personal learning style.. I do not wish anybody to give me the entire program to solve my problem, and I didn't ask for one either.

The only things I wasn't sure about that line of code was the % and <<, but now I know. Thanks for the explanation.

"I found it more helpful to learn by looking at other people's code"

I agree. the downside with that risk, especially by taking a random stranger's code, often out of context or without context, before you have a good understanding of the language, may lead to incorrect understandings.

what I would suggest is a good class / book in C, and then going through well written code pieces side by side with your book / class materials.

"going through well written code pieces"

The trouble there is: how does a novice know whether code is "well-written" or not?

And the trouble with a book is that you can't interact with it: you can't ask it to explain again; it can't look at your work to see where you're going wrong; it can't adjust to your particular strengths & weaknesses.

"what I would suggest is a good class"

Absolutely!

"And the trouble with a book is that you can't interact with it"

I guess that's why books are useful only for humans, not machines.

Per,

I guess somewhere down your rant you let this slip... just pointing it out:

And you would also know that | is a bit-and, so it will merge the bit patterns from the expression to the left, and the expression to the right.

Oops :)

George

Lol - yes, that one slipped. The expression "merge" is compatible with a bit-or, but the text before is not.