Reading and writing top arrays

**qwertysingh** · 02-05-2009

Hi Guys, I haven't used C for a while so I am abiot rusty, so I need to revert back to basics.

I want to create a logic gate sim in C and run it throug the CMD prompt.

The user will select the gate that they want, then they will be asked how many inputs for that gate(some gates can have no more than 1 input as some have to have at least 2). how do I get that value get entered from the scanf to create an array of that size, i.e, AND gate selected with 4 inputs, so therefore the array will be 4 large.

Secondly, the user will then be asked to set the values for the input(1's 0r 0's). how do I get these values using the scanf to populate the array? That is what I am having trouble with.

Then gate selected will then run a for loop on the array checking to see what it contains and then output the correct response (0 or 1). The last thing I want to know is how to Get the output value to be put into an array, where the size has been specified by the user.

e.g. User selects AND gate with 4 inputs, an array is created the size of 4. The user is asked to specify the size of the array for the output. One the gate has worked through the array the output value will be duplicated for every element in the output array.

I hope this makes sense, I have never being very good at explaining things, general pointers or code snippet would be great.

Thankyou in advance.

Archie

**esbo** · 02-05-2009

You don't really need a variable sized array just use part of a big one,
or you can use malloc to allocate an array of variable size and declare a pointer to it.

Code:

  int *buffer;

  printf ("How big do you want the gate? ");
  scanf ("%d", &i);

  buffer = (int *) malloc (i);

You might want to make it multi dimensional ad have an output array too.

[CODE]

To put a value on pin 3 for example

Code:


buffer[2]=1 //or 0 if off

That might help.

Or basically have one column reserved for the output so you would make it

a (n+1) by (2 to the power of n) array.

eg n=3 gives 4 X 8 array.

a b c |output for AND gate.
----------
0 0 0 |0
0 0 1 |0
0 1 0 |0
0 1 1 |0
1 0 0 |0
1 0 1 |0
1 1 0 |0
1 1 1 |1

**qwertysingh** · 02-05-2009

Hey, thanks for the response. I'll test what you posted in my code hopefully tomorrow. Just a quick question, no I can't remeber if I heard this right or not; but if you use an array thats apart of a big one, do the elements that do not get used default to 0?

If so won't that affect the the logic I code for the gates?

Thanks again.

**Adak** · 02-05-2009

You can set the other elements to any value you want, of course.

**esbo** · 02-05-2009

Originally Posted by qwertysingh

Hey, thanks for the response. I'll test what you posted in my code hopefully tomorrow. Just a quick question, no I can't remeber if I heard this right or not; but if you use an array thats apart of a big one, do the elements that do not get used default to 0?

If so won't that affect the the logic I code for the gates?

Thanks again.

If you declare an array globally (outside of main or any function) all the values wil initially be zero. After that the safest thing to do is to set any element you intend to use to either 0 or 1 as appropiate.

**laserlight** · 02-05-2009

Originally Posted by esbo

If you declare an array globally (outside of main or any function) all the values wil initially be zero.

Better yet, define the array as a local variable and initialise all its elements to zero, e.g.,

Code:

int values[MAX_INPUT_NUM] = {0};

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