C++ Array Value

Question

I'm trying to figure out the value of A, B and C at the end of the program. When I try to cout using for loop, I get a whole list of values. I need a matrix format only.

#include <iostream>
using namespace std;

int main()
{
    int m = 3;
    int A[m] [m] = {};
    int B[m] [m + 1] = {};
    int C[m + 1] [m] = {};

    int counter = 0, k = 2;
    
    for (int i=1; i<=m; i++)
    {
        for (int j=1; j<=m; j++) 
        {
            A[i-1][i-1] = counter;
            B[i][j] = counter;
            C[j-1][j-1] = k;
        }
        counter++;
        k += 3;
    }

    //Printing C
    //get array columns and rows
    int rows =  sizeof C/ sizeof A[0]; 
    int cols = sizeof C[0] / sizeof(int); 
      
    // Print 2d Array
    cout << "your_array data "<<endl<<endl;
    for (int i = 0; i < rows; ++i)
    {
        for (int j = 0; j < cols; ++j)
        {
            std::cout << C[i][j] << std::endl;
        }
    }

    return 0;
}

there is no `cout` in the code you posted. Please incldue a [mcve] of the code that has the problem and actual and expected output in the question — 463035818_is_not_an_ai, Nov 26 '20 at 09:24
`int A[m] [m] = {};` is not standard C++, but a compiler extention. use `std::vector` for variable sized arrays. — JHBonarius, Nov 26 '20 at 09:25
and please read this [Why aren't variable-length arrays part of the C++ standard?](https://stackoverflow.com/questions/1887097/why-arent-variable-length-arrays-part-of-the-c-standard). It should be `const int m = 3;` — 463035818_is_not_an_ai, Nov 26 '20 at 09:25
@JHBonarius actually the size is constant `3`/`4`. no need for `std::vector`, it can be considered as typo — 463035818_is_not_an_ai, Nov 26 '20 at 09:26
@idclev463035818 true.true. Still a mistake rookies often make ;) — JHBonarius, Nov 26 '20 at 09:29
In conventional C++ styling this should be `A[m][m]` with no spaces. The spaces here only serve to confuse. — tadman, Nov 26 '20 at 09:29
I've edited the question to include the cout @idclev463035818 — Mohamed Arham, Nov 26 '20 at 09:34
You'll have to do some work yourself to make the matrix. C++ is not matlab or python. You could use a library like Eigen or Boost UBLAS. — JHBonarius, Nov 26 '20 at 09:35
what output did you expect? What output did you get instead? — 463035818_is_not_an_ai, Nov 26 '20 at 09:36

score 1 · Accepted Answer · answered Nov 26 '20 at 09:48

Your A and C are

int A[3][3] = {};
int C[4][3] = {};

Then you use

int rows =  sizeof C/ sizeof A[0]; 
int cols = sizeof C[0] / sizeof(int);

to get its size. Thats

int rows = 3; 
int cols = 4;

Then in the loop

for (int i = 0; i < rows; ++i)
{
    for (int j = 0; j < cols; ++j)
    {
        std::cout << C[i][j] << std::endl;
    }
}

you have swapped values for rows and cols. C is int C[4][3]; not int C[3][4];.

If you want to print several elements in one line you just need to move the std::endl to only add a new line only after a row:

for (int i = 0; i < rows; ++i)
{
    for (int j = 0; j < cols; ++j)
    {
        std::cout << C[i][j] << " ";
    }
    std::cout << "\n";
}

Also note that this is not standard C++

int m = 3;
int A[m] [m] = {};
int B[m] [m + 1] = {};
int C[m + 1] [m] = {};

Read Why aren't variable-length arrays part of the C++ standard? for more on that.

Valerio Balzano · Answer 2 · 2020-11-26T11:16:50.210

-1

`

 for(i=0;i<rows;i++)
 {
     for(j=0;j<cols;j++)
     {
         cout<<C[i][j]<<" ";
     }
     cout<<"\n";
 }

` std:: is unnecessary because you have using namespace std; You don't have to do endl because doing this you will print the next value on the next line. So you have to put another cout out of the nested loop.

edited Nov 26 '20 at 11:16

answered Nov 26 '20 at 09:47

Valerio Balzano

11
4

2

you should explain your answer. Not just do his homework for him. – JHBonarius Nov 26 '20 at 09:52

C++ Array Value

2 Answers2