Programming Tutorials

Matrix using nested for loops in C++

By: Ignatius  

This simple C++ program illustrates the use of three nested for loops. The program multiplies matrix x and y and stores the resulting matrix product xy in matrix z. Both x and y must be compatible for multiplication that means, the number of columns of x must be equal to the number of rows of y.

#include <iostream>
using namespace std;
#define  m  3
#define  c  2
#define  n  4
int main()
{
     int i, j, k;
     // first matrix...
     int x[m][c] = {{1,2},{3,4},{5,6}};
     // second matrix...
     int y[c][n] = {{7,8,9,10},{11,12,13,14}};
     // for storing the matrix product result...
     int z[m][n];
     for(i=0; i<m; i++)
            for(j=0; j<n; j++)
            {
                   z[i][j] = 0;
                   for(k=0; k<c; k++)
                   // same as z[i][j] = z[i][j] + x[i][k] * y[k][j];
                   z[i][j] += x[i][k] * y[k][j];
            }
     cout<<"\nMultiply matrix x and matrix y,";
     cout<<"\nThen store the result in matrix z.";
     cout<<"\nMatrix x is 3x2, and matrix y is 2x4,";
     cout<<"\nso, the result, z should be matrix 3x4\n";
     cout<<"\nThe matrix product is:  \n";
     for (i=0; i<m; i++)
     {
            cout<<"\n";
            for(j=0; j<n; j++)
              // display the result...
              cout<<"   "<<z[i][j];
     }
     cout<<endl;
     return 0;
}

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