I writing a program that sum of elements in a 2D array and print out the sum.

Here my code so far:

```
#include <iostream>
#include <stdio.h>

int main()
{
    int array [3][5] = 
    {
        { 1, 2, 3, 4, 5, }, // row 0
        { 6, 7, 8, 9, 10, }, // row 1
        { 11, 12, 13, 14, 15 } // row 2
    };

    int i, j=0;
    int num_elements=0;
    float sum=0;

    for (i=0; i<num_elements; i++)
    {
        sum = sum + array[i][j];

    }

/*for(i=0; i<num_elements; i++)
   {
     printf("%d ", array[i][j]);
   }*/

    // printf("a[%d][%d] = %d\n", sum);

    // output each array element's value 
    for ( i = 0; i < 3; i++ )
    {
      for ( j = 0; j < 5; j++ )
      {
          printf("a[%d][%d] = %d\n", i,j, array[i][j]);

      }
    }

    system("PAUSE");
    return 0;
}

```

I can print out the elements in each array fine. But I want to print out the sum of elements. I tried one as you can see in the comment section but it didn't work. Can anyone help?