How to create a multi-dimension array in C Plus Plus
I need some help to create a multi-dimension array in C Plus Plus, but the user have to input the size of the array n x n.
The array has to be in simple C Plus Plus code with no class creation.
I try to make some thing like this, but dont work.
int main ()
{
int a, b;
int matriz[a][b];
cout<<"Define the size of the matrix.\n";
cin >> a;
b=a;
}
But because i´m a noob on programming i can´t make it work. Please can you give me some help or directions.
Appreciated.
1) create a array of size n, but they are pointers.
2) foreach pointer in this array, create a array to be pointed by this pointer.
int ** pa = new int [n];
for()
....
Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.
>> Most nowadays C++ compilers won't allow definition of an array with non-const size parameters
It seems I have been spoiled by g++ which supports it as an extension.
Variable length arrays are allowed in C99, but are not covered by the C++ standard. So, my initial response was correct after all (I should rely on my intuition a bit more lol).
You have to use dynamically allocated memory for variable length arrays in C++, unless you want to make use of a compiler extension like g++ has.
Yes it´s in C++.
errang, that don´t work .
I´m trying to make the game Tic Tac Toe but the user have to input the size of the matrix.
If the matrix is static is easy but they want the matrix dynamic.
I made this when i saw some examples, but i don´t understand.
#include <iostream>
using namespace std;
int main ()
{
int i=0,a,b;
int **matrix;
cout<< "Insert the size of the Matrix.\n";
cin>>a;
b=a;
matrix= new int*[a];
for (i; i<a;i++)
{
matrix[i]= new int [b];
}
system ("PAUSE");
return 0;
}
And how can i send some information to inside, i cant visualize in my mind how this works.
Thank you all.
Another approach is to just allocate it in a linear 1 dimensional array, and write an "access(arr, row, col)" method. Arrays are laid out like that anyway.
int *matrix = new int[ ROWSIZE * COLSIZE ];
int access(int * matrix, int row, int col) {
return matrix[ ROWSIZE * row + col];
}
void matriz()
{
int a,b,c=1;
int **matrix;
cout<< "Insert the size of the Matrix.\n";
cin>>a;
b=a;
for (int i=0; i<a;++i)
{
matrix= new int*[a];
for (int j=0; j<a; ++j)
{
matrix[i]= new int [b];
matrix[i][j]= c;
c++;
cout <<matrix[i][j]<<" ";
}
cout << endl;
}
}
Maybe it´s not the write way but it work.
Can you give me your feedback please.
If you agree with this way i will close this question and give the points.
Thank you all
Now, I will show you the trick I was referring to, which is something C programmers may do more than C++, but it is more memory and cache efficient than an array of pointers to arrays, and is one less level of indirection, because it allocates a single contiguous array. I'm not recommending you go this route, I would use an stl component, myself, but its worth knowing how to do this as an alternative.
void matrix()
{
int a,b,c=1;
int *matrix;
cout<< "Insert the size of the Matrix.\n";
cin>>a;
b=a;
matrix= new int[a * b];
for (int i=0; i<a;++i)
{
for (int j=0; j<a; ++j)
{
matrix[i*a + j]= c;
c++;
cout <<matrix[i * a + j]<<" ";
}
cout << endl;
}
As mrjoltcola already pointed out, there are a few problems with that code, memory leaks not being the least of it. But note that you posted correct code earlier here : http:#24059085. Why change that ?
You are doing it backwards.