+ 5
How to show matrix in c++?
42 Respuestas
+ 3
#include <iostream>
using namespace std;
int main() {
int r,c;
cin >> r;
cin >> c;
int (*matrix)[c] = (int(*)[c]) new int[r*c]; // r rows c columns
for(int i = 0; i < r; i++)
for(int j = 0; j < c; j++)
*((int*)(matrix+i)+j) = i*10 + j;
for(int i = 0; i < r; i++)
{
cout << endl;
for(int j = 0; j < c; j++)
cout << *((int*)(matrix+i)+j) << " ";
}
delete [] matrix;
return 0;
}
+ 7
What a HOT debate guys!
+ 7
Thank you Andrea and NeutronStar. I've got some value out of your analyses.
+ 6
First of all, it depends to the dementionality of your matrix. But for a simple "m * n" matrix you need to declare a 2D array and after which two for loop to access to every single element.
int arr[2][3] = { fill with some integer };
for (int i = 0; i < 2; ++i)
for (int j = 0; j < 3; ++j)
cout << arr[i][j]; // print out elements
There's another elegant way to do so, using STL vector.
std::vector<int> v(2, 75);// fill with 75
std::vector<std::vector<int> > v2d(3, v);
for (size_t i = 0; i < v2d.size(); ++i)
for (size_t j = 0; j < v2d[i].size(); ++j)
cout << v2d[i][j];
+ 4
Hi Andrea. Great snippet, but you need to add 1 into the right hand side of condition.
https://code.sololearn.com/c9OB8knZHGE3/?ref=app
+ 4
Thank you Andrea.
+ 3
You can also do this with only one loop and one pointer:
int matrix[30][50];
//fill your matrix
int *p = matrix[0];
while(p < &matrix[29][49])
cout << *p++;
+ 2
yes because i forgot =
+ 2
try p<= without +1
+ 2
also with only one line of code
for(int *p = matrix[0]; p <= &matrix[1][2] ; p++) cout << *p;
+ 2
😉😉😉
+ 2
Pointer version
#include <iostream>
using namespace std;
/* This code demonstrate implementation of 2D array as array of array */
int main() {
int const rows = 4;
int const columns = 5;
// allocate memory for rows
int** m = new int*[rows];
// for each row allocate memory for columns
for(int r =0; r<rows; r++)
{
*(m+r) = new int[columns];
}
// fill array with values
for(int r =0; r<rows; r++)
{
for(int c=0; c<columns; c++)
{
*(*(m+r)+c) = r+c;
}
}
// display the stored values
for(int r =0; r<rows; r++)
{
for(int c=0; c<columns; c++)
{
cout << *(*(m+r)+c) << " ";
}
cout << endl;
}
// for each row free the memory allocated for columns
for(int r = 0; r<rows;r++)
{
delete [] m[r];
}
// now free memory allocated for rows
delete [] m;
return 0;
}
+ 2
too much lines and things NeutronStar...learn about pointer-to-array
+ 2
#include <iostream>
using namespace std;
int main() {
int (*matrix)[10] = (int(*)[10]) new int[5*10]; // 5 rows 10 columns
for(int i = 0; i < 5; i++)
for(int j = 0; j < 10; j++)
matrix[i][j] = i*10 + j;
for(int i = 0; i < 5; i++)
{
cout << endl;
for(int j = 0; j < 10; j++)
cout << matrix[i][j] << " ";
}
delete [] matrix;
return 0;
}
+ 2
why use array of array? greater is the matrix greater is memory wasted to store all pointers to each rows
+ 2
I know that arrays decay into pointers and so one...I think that implement a matrix like a pointer to pointer is not the optimized way to implement a matrix.
+ 2
No? This app has a purpose: teach something! I know...learn how to optimize a code may be useless if you create a program to add two number having available 2Gb of RAM. But try to create something more important with few kbytes in a embedded system like Arduino and so on.
Then with your method you need:
1)more memory to store all pointers
2)much time to dereference them
And think with 3d, 4d, 5d arrays...
You dereference and dereference and...
I get an andress (matrix[0], tensor[0], 5d[0]) then I add at this address some values...then I dereference only one time. At the end, indipendently of array's dimension. Without waste memory for array of array of matrix of array of pointers and so on...
+ 2
My
*((int*)(matrix+i)+j)
is faster than your
*(*(matrix+i)+j)
because your matrix is a pointer to pointer
my matrix is a pointer to array
you dereference your matrix then you "move" it
i "move" my matrix
+ 1
The last way would be to define a class for Matrix as well, which will allow you to do something like this easily.
Matrix a;
//Define a matrix object...
cin>>a;
// Input the matrix like you do with any other integer, character, etc...
cout<<2*a;
//Print scalar multiples of a matrix as easily as this...
Matrix b;
cin>>b;
cout<<a+b<<"\n"<<a*b<<endl;
//Print sum and products of matrices easily...