How Do I Multiply Two 10x10 Arrays in C++?

Question

I'm currently trying to write a program that uses a function that takes 3 different 10x10 arrays as parameters, and fills the 3rd array with the product of the first 2 arrays.

I have scoured the web to try and figure the problem out on my own, but so far, I have only come up with this:

(I populated the first array with 2's, and the second array with 3's)

#include <iostream>

using std::cout;
using std::cin;
using std::endl;

/************************************************
** Function: populate_array1
** Description: populates the passed array with 2's
** Parameters: 10x10 array
** Pre-Conditions:
** Post-Conditions:
*************************************************/
void populate_array1(int array[10][10])
{
  int i, n;
  for (i = 0; i<10; i++)
  {
    for (n = 0; n<10; n++)
    {
      array[i][n] = 2;
    }
  }
}

/************************************************
** Function: populate_array2
** Description: populates the passed array with 3's
** Parameters: 10x10 array
** Pre-Conditions:
** Post-Conditions:
*************************************************/
void populate_array2(int array[10][10])
{
  int i, n;
  for (i = 0; i<10; i++)
  {
    for (n = 0; n<10; n++)
    {
      array[i][n] = 3;
    }
  }
}

/************************************************
** Function: multiply_arrays
** Description: multiplies the first two arrays,
and populates the 3rd array with the products
** Parameters: 3 10x10 arrays
** Pre-Conditions:
** Post-Conditions:
*************************************************/
void multiply_arrays(int array1[10][10], int array2[10][10], int array3[10][10])
{
  int i, n, j;
  for (i = 0; i<10; i++)
  {
    for (n = 0; n<10; n++)
    {
      for (j = 0; j<10; j++)
      {
        array3[i][n] += array1[i][j]*array2[j][n];
      }
    }
  }
}

int main()
{
  int array1[10][10];
  int array2[10][10];
  int array3[10][10];

  populate_array1(array1); // Fill first array with 2's
  populate_array2(array2); // Fill second array with 3's

  multiply_arrays(array1, array2, array3);

  cout << array1[5][2];
  cout << endl << array2[9][3];
  cout << endl << array3[8][4];

  return 0;
}

To my understanding, this should work, however whenever I print any of the cells within the 3rd array, I do not get 60 as seen here:

Any help would be much appreciated.

Answer 1

You need to initialize all values in array3 to 0. Its not done for you. And if you don't do that, you're using a random value as your initial value.