Help with 2d arrays

**thamiz** · 05-25-2008

Originally Posted by Elysia

You know how much data you're reading, aren't you? Then you know the width and height of your array.

Actuauly no i don't know. Because the width and height keeps changing.
my program will find find the width and height of the file. Bu the problem is i don't know how to specify the size of the resultant array.
mabye i could do it this ay, but any ideas ?
You could then have four variables: x_start, x_end, y_start, and y_end. When reading the array you would want to find these four points.

When you are finished reading you could then crop the array to everything between these co-ordinates.

**Elysia** · 05-25-2008

Take it this way: you do read data into the array, so somehow you must know the size of the array and/or data, because otherwise you wouldn't be able to read it into the array, would you?
Therefore we must logically assume that you know x_start, x_end, y_start, y_end of the array (and btw, x_start and y_start should be 0).
Then you could basically read the array, find the data you want to keep and count that. From that information, you could create a new array and copy data over.
It's not unlike any normal life situation, you just have to think over it logically. You can create a flow chart - a chart that describes how you want the process to be done, in terms of words.
That's the first step of the process. After that, you translate it into code. But let's get the first part done first.

**Adak** · 05-25-2008

Can you post a small example of how your data changes, requiring the array to change. Just something small, but something to help clarify your description.

I don't have a clear enough picture yet, in my mind.

**thamiz** · 05-25-2008

Originally Posted by Adak

Can you post a small example of how your data changes, requiring the array to change. Just something small, but something to help clarify your description.

I don't have a clear enough picture yet, in my mind.

hi there
well all the files will have a variable width of 0 to 50, and a variable height of 0 to 80. But my program can find the height and width of the file. But the problem lies when i want to start to crop that array into a new array. i don't know the width and height of the new array as i can't open the file. the program will have to somehow find the row find the row that doen't contain all 0's in its column.
hope that is enough information.
thanks in advance

**Elysia** · 05-25-2008

Originally Posted by thamiz

i don't know the width and height of the new array as i can't open the file. the program will have to somehow find the row find the row that doen't contain all 0's in its column.

But this is what we're telling you is so easy.
If you traverse and read the array, you can determine how much data you need to copy.
You have already demonstrated that you know how to traverse an array.
The next step is to make sure the program remembers how much data it needs to copy.
Then you can create a new array and copy the data over.

**thamiz** · 05-25-2008

Originally Posted by Elysia

But this is what we're telling you is so easy.
If you traverse and read the array, you can determine how much data you need to copy.
You have already demonstrated that you know how to traverse an array.
The next step is to make sure the program remembers how much data it needs to copy.
Then you can create a new array and copy the data over.

Would a counter be advisable

**Elysia** · 05-25-2008

Yes, a counter to count how many rows to copy might be advisable.

**thamiz** · 05-25-2008

Originally Posted by Elysia

Yes, a counter to count how many rows to copy might be advisable.

i have a question
say if int a counter called goodrowcounter;
when i int the array[goodrowcounter][width];
my compiler say error: variable-sized objects may not be initialiased.
what can i do to rectify this problem

**Elysia** · 05-25-2008

Originally Posted by thamiz

i have a question
say i int a counter called goodrowcounter;
when i int the array[goodrowcounter][width];
my compiler say error: variable-sized objects may not be initialiased.
what can i do to rectify this problem

You need to use malloc to create a dynamic array (don't forget to free it using free later either).

**thamiz** · 05-25-2008

Originally Posted by Elysia

You need to use malloc to create a dynamic array (don't forget to free it using free later either).

how do i use malloc

**Elysia** · 05-25-2008

Do you have a C book to learn from?

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thanks again for your patience and time

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