#include <stdio.h>
#include <math.h>
#include <stdlib.h>

int main ()
{
  int A[10];          // Statically-sized unidimensional array.
  double B[20][20];   // 2D array.

  int *A2 = NULL;     // Declaration of 1D array variable.
  double **B2 = NULL; // Declaration of 2D array variable.

  int i, j;           // For-loop variables.

  int sum;            // For use in examples.
  double dSum;      


  // Static example. The space is already allocated, so the
  // array can be used immediately.
  for (i=0; i < 10; i++) {
    A[i] = i * 100;                // Fill the array with some numbers.
  }

  sum = 0;
  for (i=0; i < 10; i++) {
    sum += A[i];                   // Compute the sum of array's numbers.
  }
  printf ("sum = %d\n", sum);      // Print sum.


  // Dynamic version of example using "malloc" to allocate space.
  // Note the use of the "sizeof" keyword.
  A2 = (int*) malloc (sizeof(int) * 10);
  for (i=0; i < 10; i++) {
    A2[i] = i * 100;               // Fill the array with some numbers.
  }

  sum = 0;
  for (i=0; i < 10; i++) {
    sum += A2[i];                  // Compute the sum of array's numbers.
  }
  printf ("sum = %d\n", sum);      // Print sum.



  // 2D example with static array.
  for (i=0; i < 20; i++) {
    for (j=0; j < 20; j++) {
      B[i][j] = i*j;               // Fill the array with some numbers.
    }
  }

  dSum = 0;
  for (i=0; i < 20; i++) {
    for (j=0; j < 20; j++) {
      dSum += B[i][j];             // Compute the sum of array's numbers.
    }
  }
  printf ("dSum = %lf\n", dSum);   // Print sum.

  
  // Dynamic version of 2D example. Note the two-step allocation.

  // Allocate space for 20 pointers-to-double
  B2 = (double **) malloc (sizeof(double*) * 20);
  for (i=0; i < 20; i++) {
    // For each such pointer, allocate a size-20 double array.
    B2[i] = (double*) malloc (sizeof(double) * 20);
  }

  for (i=0; i < 20; i++) {
    for (j=0; j < 20; j++) {
      B2[i][j] = i*j;              // Fill the array with some numbers.
    }
  }

  dSum = 0;
  for (i=0; i < 20; i++) {
    for (j=0; j < 20; j++) {
      dSum += B2[i][j];            // Compute the sum of array's numbers.
    }
  }
  printf ("dSum = %lf\n", dSum);   // Print sum.


  // Must free allocated memory when not needed anymore:
  free (A2);
  free (B2);

}