array concept - Xtreme Visual Basic Talk

07-10-2002, 08:58 PM

kinki

Guest

Posts: n/a

array concept

when we r using arrays, in arrays concept, it start from 0(index), but now i would like to start from 1, is that logic? i just write my program like this(multi dimension)
for(i=1;i<=10;i++)
for(j=1;j<=10;j++)
is that logic? how about the value of a[0][0], is that garbage value? we don't have to border ?or we should start our index 0?

07-10-2002, 09:48 PM

rich2kchan rich2kchan is offline

Centurion

Join Date: Feb 2002

Location: NY

Posts: 143

from wat ive learned so far about c++, i think the array will go out of bound if u get the index larger than the array's length:
ie. if u got an array such as this:
int array1[10,10];

then u should have allocated memory for array1[0,0] to array1[9.9]

if u try to access the variable of array1[10,10], i think it may then access the memory that is in use by other program -- not somethin u wanna do...

__________________
Richard Chan -- the wanderer in the world of insanity.
My website, for those who care.

07-11-2002, 12:36 AM

kinki

Guest

Posts: n/a

but if you start from array1[1][1], i think it will have some value in array1[10][10]?

07-11-2002, 01:02 AM

Flyguy

Lost Soul

Super Moderator
* Guru *

Join Date: May 2001

Location: Vorlon

Posts: 18,885

If you declare an array in C(++) it's range will be from 0 to maximum value -1.

Code:

int array1[5]

Will give you these 5 locations:

Code:

array1[0]
array1[1]
array1[2]
array1[3]
array1[4]

Unlike in VB you can't make an array start at position 1.

07-12-2002, 01:04 AM

kinki

Guest

Posts: n/a

but can i do like this
int array[5]
array[1]=1
array[2]=2
array[3]=3
array[4]=4
array[5]=5

is this logic?

07-12-2002, 01:26 AM

Flyguy

Lost Soul

Super Moderator
* Guru *

Join Date: May 2001

Location: Vorlon

Posts: 18,885

Huh????

You are really missing the point.
I told you when you do:

Code:

int array[5] 
array[0]=1 
array[1]=2 
array[2]=3 
array[3]=4 
array[4]=5

array[5] does NOT exist

07-13-2002, 07:19 AM

Rezner

C# Lover

* Expert *

Join Date: Jan 2002

Location: 00-80-C8-C3-2E-52

Posts: 1,899

ArountV is correct. array[5] does not exist. If you attempt to access it, you are going to get an unpredictable garbage value with most compilers). This is because you are pointing to a memory address that has not been given any value... so you will never know what is in there.

You *could* start the index at 1 if you absolutely wanted to. Use something like:

Code:

 int intElements;

 cout << "How many elements in the array? ";
 cin >> intElements;

//since you want to skip the 0 index, 
//you must carve out an array with 
//its size being one element larger than normal
 int *wow = new int[intElements+1];

//for demonstration purposes,
//give the array elements a value that 
//corresponds with its index
//(notice that index 0 is skipped and never initialized)
 for (int x=1; x<=intElements; x++)
   wow[x] = x;

//for demonstatration purposes,
//display the values by accessing the 
//corresponding index
 for (int x=1; x<=intElements; x++)
        cout << wow[x] << endl;

//just for the heck of it, see what's in the 0 index
cout << wow[0];

Here's the output I got with my Borland compiler.

Code:

How many elements in the array? 5
1
2
3
4
5
23981055

__________________
"Man is still the best computer we can put aboard a spacecraft...and the only one that can be mass produced with unskilled labor." - Wernher von Braun

Last edited by Rezner; 07-13-2002 at 07:26 AM.

09-04-2002, 07:13 PM

Junebug

Guest

Posts: n/a

In order to force the array to start at 1, include this statement:
Option Base 1
Regards,
Bobbi (Junebug)

09-04-2002, 07:22 PM

orufet

Paranoid Coder

Retired Leader

Join Date: Mar 2001

Location: Canada

Posts: 2,716

"Option Base 1" is for Visual Basic, not C++.....

#10

09-04-2002, 08:01 PM

noRulez

Contributor

Join Date: Aug 2002

Location: Kansas

Posts: 502

If you're a Computer Science student you had better learn to start counting from zero. It will just come back to haunt you over and over again if you don't. It's a concept that is best learned early. You get used to it after a while. Also, if you plan on doing any programming at all, you should get comfortable with the idea...not just if you're a computer science student.

__________________
"As far as the laws of mathematics refer to reality, they are not certain; as far as they are certain, they do not refer to reality."--Albert Einstein

#11

09-05-2002, 05:31 AM

quwiltw

Junior Contributor

Join Date: Sep 2001

Location: Washington, D.C.

Posts: 302

While Rezner provides a creative way to make a 1 based array, if you're ever going to write code that has a chance of being seen by anyone other than yourself, please don't do this. Most people are used to, and quite comfortable with, 0-based arrays in C++ to do otherwise would only serve to confuse people.