将2D数组复制到C ++中未知大小的其他2D数组

Question

I have a question about dynamic 2D array returning. That means I don't know size of returning 2D array (It depends on some condition). Let see my problem

N=3; 
A[N][5]={}//Given a 2D array
for i=1 to N
   x=random between 0 and 1
   k=1;
   while(k<N&&x>0.3)

    k++;
    B_i=A_k //Look like copy value of array A to array B at position k

My problem is that I don't know the value of k, it depends on (k<N&&x>0.3) . Hence, I cannot initial the array B. Could you suggest to me one way to do it? This is my code that I tried

int A[2][5] =
    {
        {1,8,12,20,25},
        {5,9,13,24,26},
        {15,1,5,2,22}
    };


int N=3;
   for(int i=0;i<N;i++) 
   {
   double x=random();//create random number between 0 and 1.
   int k=0;
   while(k<N&&x>0.3)
     {
     k++;
     B[k][4]=A[i][4]; //I have no idea to initial 2D array B
     }
   }

Answer 1

you may use

std::vector<std::vector<int>> B;
st::vector<int> row;
row.push_back(1);
row.push_back(2);
B.push_bak(row);

st::vector<int> row1;
row1.push_back(3);
row1.push_back(4);
B.push_bak(row1);

in this way you will get array {{1,2},{3,4}} or

int** B;
B = new int*[2];
B[0]=new int[2];
B[1]=new int[2];

B[0][0] =1;
B[0][1] =2;
B[1][0] =3;
B[1][1] =4;

Answer 2

Maybe you could use the fact k can not become larger than N?

The loop

while(k<N && x>0.3)
 k++;

will always terminate when/if k becomes equal to N (regardless of x) so the array B should be

int B[N+1][5];    

EDIT: Just to clarify - the point is that k will alway be in the range [1..N]. I didn't want to state that k would always become N. Only that k could not be greater than N.

Answer 3

vector< vector<int> > A;    
int N=3;
   for(int i=0;i<N;i++) 
   {
   double x=random();//create random number between 0 and 1.
   int k=1;
   while(k<N&&x>0.3)
     k++;
   B.push_back(A[i]);
   }