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Jun 20th, 2008

The Char Data Type with 1 vs 2 Dimensional Array

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Hey, here are two codes and with one slight difference they do different things
CODE 1

C++ Syntax (Toggle Plain Text)
 #include<iostream>
using namespace std;
int main()
{
char array[2];
int i=0;
while (i<2)
{
cin>>array[i];
i++;
}
cout<<array[0]<<' '<<array[1];
}
 #include<iostream>
using namespace std;
int main()
{
char array[2];
int i=0;
while (i<2)
{
cin>>array[i];
i++;
}
cout<<array[0]<<' '<<array[1];
}

EXAMPLE OUTPUT:

C++ Syntax (Toggle Plain Text)

two words
t w

CODE 2

C++ Syntax (Toggle Plain Text)
 #include<iostream>
using namespace std;
int main()
{
char array[2][100];
int i=0;
while (i<2)
{
cin>>array[i];
i++;
}
cout<<array[0]<<' '<<array[1];
}
 #include<iostream>
using namespace std;
int main()
{
char array[2][100];
int i=0;
while (i<2)
{
cin>>array[i];
i++;
}
cout<<array[0]<<' '<<array[1];
}

EXAMPLE OUTPUT:

C++ Syntax (Toggle Plain Text)

two words
two words

How is that occurring, by adding an extra dimension to array it takes both words. What is going on....lol

Thanks!

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salman213

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Jun 20th, 2008

Re: The Char Data Type with 1 vs 2 Dimensional Array

>How is that occurring, by adding an extra dimension to array it takes both words.
It helps to know that the native string type in C++ is actually an array of char, and cin's >> operator is pretty smart about knowing what types you give it. When array[i] is an array of char, cin>>array[i]; will read a word into it. when array[i] is a single char, cin>>array[i]; will read a single character into it.

Narue

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Jun 20th, 2008

Re: The Char Data Type with 1 vs 2 Dimensional Array

You need to read a basic tutorials on arrays... Seeing this is c++ have a look at std::strings as well.

Last edited by iamthwee; Jun 20th, 2008 at 5:14 pm.

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Jun 20th, 2008

Re: The Char Data Type with 1 vs 2 Dimensional Array

is it possible to think of it as a matrix?

for example

C++ Syntax (Toggle Plain Text)
char array[2][2];
char array[2][2];

Isn't this what we are forming

C++ Syntax (Toggle Plain Text)
      0     1 
0   
 
1
      0     1 
0   
 
1

If we do

C++ Syntax (Toggle Plain Text)
cin>> array[0]
cin>> array[0]

and we input the word: "WHAT"
how is that being placed in to the matrix I drew.

To display the word I played around and found I can do this:

C++ Syntax (Toggle Plain Text)
cout<< array[0][0]<<array[0][1]<<array[0][2]<<array[0][3]
cout<< array[0][0]<<array[0][1]<<array[0][2]<<array[0][3]

But I thought the maximum it can go to was array [1][1] ?? So how can those arrays be defined.

I mean the only combinations I thought were possible according to a tutorial I read were

array[0][0]
array[0][1]
array[1][0]
array[1][1]

Last edited by salman213; Jun 20th, 2008 at 5:53 pm.

salman213

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Jun 20th, 2008

Re: The Char Data Type with 1 vs 2 Dimensional Array

Click to Expand / Collapse Quote originally posted by salman213 ...

is it possible to think of it as a matrix?

for example
C++ Syntax (Toggle Plain Text)
char array[2][2];
char array[2][2];
Isn't this what we are forming
C++ Syntax (Toggle Plain Text)
      0     1 
0   
 
1
0 1 0 1
If we do
C++ Syntax (Toggle Plain Text)
cin>> array[0]
cin>> array[0]
and we input the word: "WHAT"
how is that being placed in to the matrix I drew.

To display the word I played around and found I can do this:
C++ Syntax (Toggle Plain Text)
cout<< array[0][0]<<array[0][1]<<array[0][2]<<array[0][3]
cout<< array[0][0]<<array[0][1]<<array[0][2]<<array[0][3]
But I thought the maximum it can go to was array [1][1] ?? So how can those arrays be defined.

I mean the only combinations I thought were possible according to a tutorial I read were

array[0][0]
array[0][1]
array[1][0]
array[1][1]

When the compiler saw this line:

C++ Syntax (Toggle Plain Text)
char array[2][2];
char array[2][2];

it set aside memory for 2 x 2 = 4 bytes of contiguous memory. Let's say it stored array[0][0] at the following address in memory:

C++ Syntax (Toggle Plain Text)

0xaa0000

The four characters would be stored at the following addresses:

C++ Syntax (Toggle Plain Text)
array[0][0]   0xaa0000
array[0][1]   0xaa0001
array[1][0]   0xaa0002
array[1][1]   0xaa0003
array[0][0]   0xaa0000
array[0][1]   0xaa0001
array[1][0]   0xaa0002
array[1][1]   0xaa0003

If you are referring to the element array[i][j], the computer figures out which address in memory is being referred to by this mathematical equation:

C++ Syntax (Toggle Plain Text)
address = address of array[0][0] + offset
address = address of array[0][0] + offset

where offset is calculated as:

C++ Syntax (Toggle Plain Text)

(i times number of rows) + j

In your case the number of rows = 2, so offset is:

C++ Syntax (Toggle Plain Text)

offset = 2i + j

So in the case of array[0][3], i = 0 and j = 3, so:

C++ Syntax (Toggle Plain Text)
offset = 0 * 2 + 3 = 3
offset = 0 * 2 + 3 = 3

The address of array[0][3] is thus:

C++ Syntax (Toggle Plain Text)

0xaa0000 + 3 = 0xaa0003

which is the address of array[1][1], so array[1][1] and array[0][3] are equivalent here, so when you displayed array[0][3], you were really displaying what was stored at array[1][1], which is 'T'.

However, even though you can get away with it, it's probably not a great habit to get into and you should probably only reference the elements array[0][0], array[0][1], array[1][0], and array[1][1].

VernonDozier

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Jun 20th, 2008

Re: The Char Data Type with 1 vs 2 Dimensional Array

alright thanks alot for explaining so clearly.

cool..

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