Question

I’m new to C++ programming. I need to sort this matrix:

#include <iostream>
#include <iomanip>


#include <cstdlib>

using namespace std;


int main(int argc, char** argv) {

    Mat10 a;
    fillRand(a, 5, 5);
    prnMat(a, 5, 5);
    cout << endl;

    return 0;
}

void fillRand(Mat10 m, int n, int k) {
    for (int i = 0; i < n; i++)      
        for (int j = 0; j < k; j++)
            m[i][j] = rand() % 1000;    
}

void prnMat(Mat10 a, int m, int n) {
    for (int i = 0; i < m; i++) {        
        for (int j = 0; j < n; j++)
            cout << setw(8) << a[i][j];
        cout << endl;
    }
}

I need to sort the matrix from the beginning from the beginning. The smallest value must be at the beginning of the of the first column. The next must be below it and so on. The result must be sorted matrix – the smallest number must be at the beginning of the left column – the biggest value must be at the end of the matrix. Would you please help to solve the problem?

EDIT

Maybe I found possible solution:

void sort(int pin[10][2], int n)
{
    int y,d;
    for(int i=0;i<n-1;i++)
    {
        for(int j=0; j<n-1-i; j++)
        {
            if(pin[j+1][1] < pin[j][1])  // swap the elements depending on the second row if the next value is smaller
            {
                y = pin[j][1];
                pin[j][1] = pin[j+1][1];
                pin[j+1][1] = y;
                d = pin[j][0];
                pin[j][0] = pin[j+1][0];
                pin[j+1][0] = d;
            }
            else if(pin[j+1][1] == pin[j][1]) // else if the two elements are equal, sort them depending on the first row
            {
                if(pin[j+1][0] < pin[j][0])
                {
                    y = pin[j][1];
                    pin[j][1] = pin[j+1][1];
                    pin[j+1][1] = y;
                    d = pin[j][0];
                    pin[j][0] = pin[j+1][0];
                    pin[j+1][0] = d;
                }
            }
        }
    }
}

But since I’m new to programming I don’t understand is this the solution?

Answer 1

Here is a simple example for you:

#include <vector>
#include <algorithm>

using namespace std;

//This is the comparation function needed for sort()
bool compareFunction (int i,int j) 
{ 
    return (i<j); 
}

int main()
{
    //let's say you have this matrix
    int matrix[10][10];
    //filling it with random numbers.
    for (int i = 0; i < 10; i++)
        for (int j = 0; j < 10; j++)
            matrix[i][j] = rand() % 1000;

    //Now we get all the data from the matrix into a vector.
    std::vector<int> vect;
    for (int i = 0; i < 10; i++)
        for (int j = 0; j < 10; j++)
            vect.push_back(matrix[i][j]);

    //and sort the vector using standart sort() function
    std::sort( vect.begin(), vect.end(), compareFunction );

    //Finally, we put the data back into the matrix
    for (int i = 0; i < 10; i++)
        for (int j = 0; j < 10; j++)
            matrix[i][j] = vect.at(i*10 + j);
}

After this, the matrix will be sorted by rows:

1 2
3 4

If you want it to be sorted by cols:

1 3
2 4

You need to replace matrix[i][j] in the last cycle only with matrix[j][i]

If you need to read about the the sort() function, you can do it here
Hope this helps.