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Error: Dynamic Multidimensional Array

Posted on 2003-12-10
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Last Modified: 2008-02-01

Hi,

I'm new to C++ and on the web I found a rather long-winded way to define multidimensional arrays.  I tweaked it into my code but I'm getting an error.  What's wrong?

-------------- SECTION OF CODE ---------------------

/*NOTE n = integer passed into function as variable
           sigma = multidimarray passed into function*/
   
double w;
double y;

//sigma (rows, columns)
w = sigma[0][0];
y = sigma[n][0] - w + 1;
       
//Create dataarray[y][1]
double ** dataarray;
dataarray = new double *[y];
dataarray[0]= new double[y*1];
for (i=1;i<y;i++) {
dataarray[i]=dataarray[i-1]+1;
}

//populate rates in column 2 of dataArray
for(i=0; i<=n; i++)
{
x = sigma[i][0];
dataarray[(x-w+1)][1] = sigma[i][1];
}

-------------- ERROR MESSAGE --------------------

D:\test.cpp(482) : error C2108: subscript is not of integral type
D:\test.cpp(482) : error C2440: '=' : cannot convert from 'double' to 'double *'
        There is no context in which this conversion is possible

-------------------------------------------------------

NOTE: Line 182 is the second last line beginning "dataarray[("

Thanks,
Malcolm


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Question by:malramsay
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8 Comments
 
LVL 10

Expert Comment

by:Sys_Prog
ID: 9918251
Hi,

-------------- ERROR MESSAGE --------------------

>>>>>>D:\test.cpp(482) : error C2108: subscript is not of integral type
>>>>>>D:\test.cpp(482) : error C2440: '=' : cannot convert from 'double' to 'double *'
        There is no context in which this conversion is possible



An array index should be integral, U are tryin with a double

HTH

Amit

0
 

Author Comment

by:malramsay
ID: 9918275

Hi again Amit,

In this code several times I need to create dynamic multidimensional arrays where all the values in those arrays are doubles.  Is there a way to do this?

I read up about a "Little Template Library (LTL)" that had MArray in it, but I'm not sure if that's the best method.  Is there some other way?

Cheers,
Malcolm
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LVL 10

Expert Comment

by:Sys_Prog
ID: 9918285
Hi

I meant the array index should be integral

U can definitely have double arrays i.e. Array in which all values are double

HTH

Amit


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LVL 10

Accepted Solution

by:
Sys_Prog earned 400 total points
ID: 9918292
This would let create multi dimenison double array

      double **arr ;
      int rows ;
      int cols ;
      cout << "Enter no of rows " ;
      cin >> rows ;
      cout << "Enter no of cols " ;
      cin >> cols ;
      
      arr = new ( double * ) [rows] ;
      
      for ( int i = 0 ; i < rows ; i ++ )
          arr [i] = new double [cols] ;


HTH

Amit
0
 

Author Comment

by:malramsay
ID: 9918340
Thanks for that Amit,

I got this to work (slight variation with n*n array), but I haven't checked the answers,

double ** a;
a=new double *[n];
for (i=0;i<n;i++) {
a[i] = new double [n] ;
}

The main difference is changing (from your code),

arr = new ( double * ) [rows] ;

to

arr = new double * [rows] ;

should that make a difference?
0
 
LVL 10

Expert Comment

by:Sys_Prog
ID: 9918373
No, that won't make a difference
0
 

Author Comment

by:malramsay
ID: 9918378

Thanks again Amit!

Thanks also Axter.  I'll check out your site - it seems to have lots of interesting stuff on there for c++ newbies.
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