Thread: Multi-level logic gates for begginers

Originally Posted by Pinkysuavo

Inputs (and all the circuit description) must come from a textfile

You might want to read algorism's post #14 again.

Basically, while the input may ultimately come from a text file, there a few ways by which that can happen. For example:

• You can hard code a specific file name in your program, then open the file with that name.
• You can allow the user to provide a file name at run time. This is typically done either by having the user provide the file name as a command line argument, or by interactively requesting the file name as input from the user. You then open the file with the name provided.
• You can read from standard input, then redirect input from the file.

I don't have a textbook. I'm reading and practicing (via internet articles, tutorials and videos) now but I still stay in the same place with the project. I mentioned the things we had discussed on classes, but I mentioned also that I don't know too much. On the classes we had some stuff but it has totally nothing to do with the project. And I won't buy a book anymore cause we move to C++ in next semester. Even if I write somehow this project I don't know how I'll deal in second semester with programming. I'm planning to practice more (in this semester I didn't do much). Also it would suck that I've dealt pretty good with other subjects and didn't pass cause of programming. I feel like this thing is not for me - I have tried like a year ago learning C++ on my own, and I stopped quite fast. Same with Pascal. Now I both want and must learn programming but it's just so complex for me.
Nevermind, gotta learn. I'll be trying to do this til the end. If I don't finish this then well it's not for me

This problem seems to be a fairly interesting exercise though: just keep going. I would start experimenting with either the reading, or the logic gate resolving. Nominal Animal's post #3 outlines an approach that I would have taken, though it is far more complex that I would suggest for you given your skills at this time.

Simplify:

• Assume that each logic gate is already resolved to TRUE or FALSE, or consists of a name and one (e.g., for the NOT gate) or two inputs (e.g., for the AND gate). This simplifies your reading of the input and allows you to get rid of the suggested inputs and input_gate members.
• Assume that there is a fixed, small number of gates. This allows you to have a plain old fixed-size array instead of doing dynamic memory allocation, and perhaps rather importantly it simplifies your reading of the input.
• Use an iterative approach to resolving the gates: "Iterative is slower (as it does several passes over all gates), but it is deterministic and has no weak spots (except for slowness). You do passes over all gates in UNKNOWN state, resolving them if none of their inputs are in unknown state. You are done when the pass no longer resolves any new gates. If there are gates left in UNKNOWN state, the graph is unresolvable (cyclic)."

If it turns out that your requirements are more complex, that's fine: having acquired the experience writing this simplified program, you will be far better equipped to writing the more complex program than if you were to try writing the more complex program now.

Originally Posted by Nominal Animal

To get you started, consider these enumerated constants, structure, and global variables:

I recommend against the use of global variables here, even though for this case the gates may indeed be global state. Rather, practice the use of local variables, parameter declarations, and argument passing.

Sry again for double post but seems like I've been writing and analysing this for over an hour, and it's not possible to edit after this period of time.

PS I still don't know how I can read the textfile storing everything. I thought I can do it somehow with fscanf or anything but the one method in higher posts - I didn't understand it at all. Maybe some article about reading files will help me out there. I'll try to find it.

PS2 Today I'll probably ask a lot of question. Even the most dumbest ones. Of course I'll try to find answers in the Internet also, not to spam here, but won't things be more clear if I learn from different sources and ,,point of views"? I'm determined to do this and I'll do anything I can to finish this project. I will do at least something today and slowly get to the end - I still have one week or even more!
I'll give now my ideas and my thoughts about what exactly these things would do. I'll try to explain what is happening in my brain to try to let you know what I understand it like. I'll also ask some questions:

1) Take a look at this structure:

Code:

typedef struct gate
{
int gate_number;
char gate_type;
int input1;
int input2;
int output;
} gate;

(does it even make sense?)
I don't understand tho why you guys used typedef for it. I mean... Consider looking at these 2 struct and typedef articles:
Structures in C
typedef in C
Either I am really dumb or I just can't see any bigger difference.
Is the difference about ,,struct" word while declaring? That's all? If yes, then I understand it I guess, if not, please explain (at first I wanted to post it without typedef but I'll just leave it)
Now my thoughts about what's the point of this structure. It can be used to store information about gates (lines in file), like when I'd fscanf it then it would ascribe 001 to gate_number[0] (we got to point when I start understanding idea of arrays here I think!), then for example A (AND) to gate_type[0] etc. Is my way of thinking fine?


2) Enumerated constants
I admit I didn't know what enumerated constans were when you first mentioned it. (PS. I'm sorry but I didnt understand algorism's idea in #4 post with the ,,left" and ,,right" variables. Yesterday I thought I get it but now I got kinda mindblown with that).

So here's it:

Code:

typedef enum gate_type
{
    gFalse = 0,
    gTrue = 1,
    gNot = 2,
    gAnd = 3,
    gOr = 4,
    gXor = 5,
} gate_type;

And also: Does it make sense? But wait a sec. Before I declared gate_type as a character. And we have numbers here. I start getting lost. How to get these 2 things together?
Let's say we have a line
001 FALSE
After reading it and getting words to different variables (I don't know yet how to do it, but let's say I do) we have a 001 integer then string FALSE. With strcmp I can check if the string is FALSE/TRUE/AND/... etc. (Wait a second, will I have write somewhere like 6 ifs about checking what's that string?)
Well, let say I detect FALSE - and if it's FALSE then it gets set up as gate_type[0]=gFalse=0.
Okay I thought I got this kinda all together but at this point I got a little lost. What does it give me? We have a line with 001 gFalse=0 but what about inputs and outputs of this line? Should I add enumerated logic value constans? Maybe something like

Code:

typedef enum logic_state
{
    lUnknown = 2, // I wanted to set it 0 as first, but prolly true and low would be confusing for me
    lLow = 0, // low as 0 is more clearer to me
    lTrue = 1, //same about 1 as true
} logic_state;

Okay, if my way of thinking is at least a little correct, this enumerated constants can help me a little. From 001 FALSE I have something like
001 gFalse lUnknown lUnknown lUnknown (as nr/type/input1/input2/output)
But I can do something like, when gate_type = g_False then output = lLow.
So I have
001 gFalse lUnknown lUnknown lLow
And the unknowns will stay as they are. Although I am not sure if this would be a good solution...
Okay, I've been writing this post for a while and I got confused a little. Not sure if this all made any sense. Please tell me what you think.

Originally Posted by Pinkysuavo

Sry again for double post but seems like I've been writing and analysing this for over an hour, and it's not possible to edit after this period of time.

This is correct. You have about an hour window to make sure your post is correct. This decision was made because people would make threads, get their answers, and then edit their original post to say something unhelpful, like "problem solved." This robbed the thread of its original context. So, it was fixed this way.

PS2 Today I'll probably ask a lot of question. Even the most dumbest ones. Of course I'll try to find answers in the Internet also, not to spam here, but won't things be more clear if I learn from different sources and ,,point of views"? I'm determined to do this and I'll do anything I can to finish this project. I will do at least something today and slowly get to the end - I still have one week or even more!

I admit I've skimmed the thread a little more than perhaps I should have. The thing we don't want to have happen is that you would cross-post to other forums, just to see who answers first. It's rude considering the time and effort people have to put into answering (consider one person at least created a small program to help you with your project). Another important point is that you might end up confused by all the different forums' advice, ending up with a terrible body of source, consisting of patchwork, when working mostly with one forum would have resulted in something more robust.

Here we appreciate a good faith effort, so if you continue to post links to other sources, and ask clear questions you will get lots of help. I think you've earned a code review if you have any of your own source code to post for the project.

I'll give now my ideas and my thoughts about what exactly these things would do. I'll try to explain what is happening in my brain to try to let you know what I understand it like. I'll also ask some questions:

1) Take a look at this structure:

Code:

typedef struct gate
{
int gate_number;
char gate_type;
int input1;
int input2;
int output;
} gate;

(does it even make sense?)
I don't understand tho why you guys used typedef for it. I mean... Consider looking at these 2 struct and typedef articles:
Structures in C
typedef in C
Either I am really dumb or I just can't see any bigger difference.
Is the difference about ,,struct" word while declaring? That's all? If yes, then I understand it I guess, if not, please explain (at first I wanted to post it without typedef but I'll just leave it)

Well, the effect is pretty small in itself. The problem that the typedef here solves is that struct becomes a nuisance word in C, but the keyword is necessary for the compiler to distinguish user-defined types from nonsense. Typedef solves this problem because it declares an alias for the original type name.

Without the typedef the way to make a gate is to say "struct gate foobar;" With the typdef, you just write "gate foobar;" and be done with it. After making say 100 gates, perhaps not all in an array, the savings to your fingers adds up.

It is important to note that some people do find separating the two statements to be cleaner, but less compact:

Code:

struct gate
{
int gate_number;
char gate_type;
int input1;
int input2;
int output;
};

typedef struct gate gate;

Now my thoughts about what's the point of this structure. It can be used to store information about gates (lines in file), like when I'd fscanf it then it would ascribe 001 to gate_number[0] (we got to point when I start understanding idea of arrays here I think!), then for example A (AND) to gate_type[0] etc. Is my way of thinking fine?

Your thinking is not really correct, but it is something the compiler would catch right away if you tried to write it.

It is important to remember that each element will have its own collection of variables. Take a look at this:

Code:

 gate full_adder[MAX_GATES]; // MAX_GATES should be at least enough gates to make this.

Now if we wanted to access the first gate we would write "gate[0]" and then accessing that gate's parts works by writing "gates[0].gate_number".

2) Enumerated constants
I admit I didn't know what enumerated constans were when you first mentioned it. (PS. I'm sorry but I didnt understand algorism's idea in #4 post with the ,,left" and ,,right" variables. Yesterday I thought I get it but now I got kinda mindblown with that).

So here's it:

Code:

typedef enum gate_type
{
    gFalse = 0,
    gTrue = 1,
    gNot = 2,
    gAnd = 3,
    gOr = 4,
    gXor = 5,
} gate_type;

And also: Does it make sense? But wait a sec. Before I declared gate_type as a character. And we have numbers here. I start getting lost.

It makes sense. char can be used here since characters are actually small, single-byte integers. Characters only behave the way they do because they are specially treated by C's standard libraries.

How to get these 2 things together?
Let's say we have a line
001 FALSE
After reading it and getting words to different variables (I don't know yet how to do it, but let's say I do) we have a 001 integer then string FALSE. With strcmp I can check if the string is FALSE/TRUE/AND/... etc. (Wait a second, will I have write somewhere like 6 ifs about checking what's that string?)
Well, let say I detect FALSE - and if it's FALSE then it gets set up as gate_type[0]=gFalse=0.
Okay I thought I got this kinda all together but at this point I got a little lost. What does it give me? We have a line with 001 gFalse=0 but what about inputs and outputs of this line? Should I add enumerated logic value constans? Maybe something like

Code:

typedef enum logic_state
{
    lUnknown = 2, // I wanted to set it 0 as first, but prolly true and low would be confusing for me
    lLow = 0, // low as 0 is more clearer to me
    lTrue = 1, //same about 1 as true
} logic_state;

Okay, if my way of thinking is at least a little correct, this enumerated constants can help me a little. From 001 FALSE I have something like
001 gFalse lUnknown lUnknown lUnknown (as nr/type/input1/input2/output)
But I can do something like, when gate_type = g_False then output = lLow.
So I have
001 gFalse lUnknown lUnknown lLow
And the unknowns will stay as they are. Although I am not sure if this would be a good solution...
Okay, I've been writing this post for a while and I got confused a little. Not sure if this all made any sense. Please tell me what you think.

So you wrote a lot here, but I don't think you asked very much.

1. When you read a file, you will need somewhere to store the information. This information can be rather complex at first and pared down to simpler results later on, but the point stands. Part of the task is determining what information you have. So yes, somewhere you will be comparing a bit of string from the file to all of the possibilities, discovering how to adjust the logic state variable.

2. It's important to remember what logic state is for. You are going to have logic state inputs that you turn, through a series of gates, into logic state outputs.

This means at a minimum you will have some small bits of logic state that start out somewhere:

Code:

 logic_state output1 = lUnknown, output2 = lUnknown, output3 = lUnknown;

You will want to follow the file as close as possible. If all of the inputs are false then you want them to start false. The only reason you start as unknown is because you want to have the opportunity to look ahead in the graph of gates and determine if there is a cycle.

If you don't understand that, then imagine the inputs flowing from one gate to the next. What you want to avoid is the situation like this:

0 HIGH
1 XOR 0 2
2 XOR 0 1

So you Start out HIGH. The first XOR would make the bit LOW and it instructs you to the next gate. That gate takes the bit that is LOW and makes it HIGH, and takes you to the first gate. So the ultimate result is unknown -- the same two gates will keep flipping the bit, and you can't break this circle. So you would error out and exit in the best of circumstances.

If you look ahead and determine there is no cycle, then you switch output1, output2, and output3 in the example above this one to FALSE, and go.

Hope this helps.

I admit I've skimmed the thread a little more than perhaps I should have. The thing we don't want to have happen is that you would cross-post to other forums, just to see who answers first. It's rude(...)

I'm sorry, I don't want to be rude. This forum is the only one I use. I use internet to search for articles when some detail is not clear for me, like for example usage of typedef was in this case.

If you don't understand that, then imagine the inputs flowing from one gate to the next. What you want to avoid is the situation like this:

0 HIGH
1 XOR 0 2
2 XOR 0 1

So you Start out HIGH. The first XOR would make the bit LOW and it instructs you to the next gate. That gate takes the bit that is LOW and makes it HIGH, and takes you to the first gate. So the ultimate result is unknown -- the same two gates will keep flipping the bit, and you can't break this circle. So you would error out and exit in the best of circumstances.

If you look ahead and determine there is no cycle, then you switch output1, output2, and output3 in the example above this one to FALSE, and go.

I don't understand you here, after the point 2.. I start out HIGH but why first XOR would make the bit LOW? I understand that there a infinit loop appears, as you said, but I don't know why would the outputs1,2,3 be false? I think I don't understand what you're trying to explain me. I'm sorry.

Code:

// read the first two values from the current line    
          while (fscanf(file, "%d %s", &i, gate_type_string) == 2) {
 
        // The gate number, i, is used as the index into the gates array
 
        gates[i].type = gate_type_string[0];  // first character is type code

 
       // Now that you have the type, you can determine

       // if you need to read any more integers from the line

I got stuck here. I made a textfile

Code:

001 TRUE
002 AND 1 3
003 FALSE

And I was trying to check different stuff. I could check that the first line has a true value but it always stopped there. I tried to create something like: when fscanf=3 then detect also the input 1, or when its equal to 4 to detect input 1 and input2 and get these things to arrays. But I failed. Usually it just ended on reading first line. I'm still mixing it but I'm starting to get confused.