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array in c++

Hi there,

I have 2dim array which have huge number I have no idea about number my question is How can I initialize this array if not are there any different way like array list in Java which is accept two dim and extend automatically
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obad62
Asked:
obad62
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1 Solution
 
phoffricCommented:
In c++, if you say:
     int arr2d[3][4] = {0};
then every element of the array will be initialized to 0.
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phoffricCommented:
If you say:
    int arr2d[3][4] = {5};
then arr2d[0][0] will be set to 5, and all the other elements in the array will be set to 0.
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phoffricCommented:
If you want to be able to extend an array, then I recommend using vector.
    http://www.cplusplus.com/reference/stl/vector/

There are various ways to construct/initialize a vector.
    http://www.cplusplus.com/reference/stl/vector/vector/

For example:
    vector<int> second (4,100);      // four ints with value 100

Below is the sample code for the vector constructor link.

To extend the array (without worrying about whether it needs extending), you can just add elements to the vector using push_back.
      http://www.cplusplus.com/reference/stl/vector/push_back/
// constructing vectors
#include <iostream>
#include <vector>
using namespace std;

int main ()
{
  unsigned int i;

  // constructors used in the same order as described above:
  vector<int> first;                                // empty vector of ints
  vector<int> second (4,100);                       // four ints with value 100
  vector<int> third (second.begin(),second.end());  // iterating through second
  vector<int> fourth (third);                       // a copy of third

  // the iterator constructor can also be used to construct from arrays:
  int myints[] = {16,2,77,29};
  vector<int> fifth (myints, myints + sizeof(myints) / sizeof(int) );

  cout << "The contents of fifth are:";
  for (i=0; i < fifth.size(); i++)
    cout << " " << fifth[i];

  cout << endl;

  return 0;
}

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phoffricCommented:
Above was a 1D discussion of vectors. Here's a thread needing a 2D vector:
     http://w.e-e.com/pJzEMB
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evilrixSenior Software Engineer (Avast)Commented:
If you want a simple 2D array, Boost's ublas library offers a simple to use matrix.
http://www.boost.org/doc/libs/1_38_0/libs/numeric/ublas/doc/matrix.htm

If you matrix is huge it is worth considering the sparse version.
http://www.boost.org/doc/libs/1_38_0/libs/numeric/ublas/doc/matrix_sparse.htm
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