Assignment 1

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/wait.h>
#include <sys/shm.h>

int main ()
{
  int i, j, row, col, id;
  int status = 0;

  row = 4;
  col = 4;

//default test matrices
  int M[4][4] = {
    {10, 20, 30, 40},
    {5, 6, 7, 8},
    {4, 3, 2, 1},
    {8, 7, 6, 5}
  };

  int N[4][4] = {
    {10, 30, 50, 70},
    {2, 4, 6, 8},
    {7, 3, 5, 7},
    {8, 6, 4, 2}
  };

  int Q[4][4] = {
    {0, 0, 0, 0},
    {0, 0, 0, 0},
    {0, 0, 0, 0},
    {0, 0, 0, 0}
  };

  int shmid;
  srand ((unsigned int) getpid ());
  // get a shared memory id of 2D array with size of 4 * 4
  shmid = shmget ((key_t) 1234, sizeof (int[4][4]), 0666 | IPC_CREAT);

  // check is the memory failed
  if (shmid == -1)
    {
      fprintf (stderr, "shmget failed\n");
      exit (EXIT_FAILURE);
    }
  // allocate the memory
  int *shared_memory = (int *) shmat (shmid, 0, 0);
  if (shared_memory == (void *) -1)
    {
      fprintf (stderr, "shmat failed\n");
      exit (EXIT_FAILURE);
    }
  // initialize the shared memory
  for (int i = 0; i < 4; i++)
    {
      for (int j = 0; j < 4; j++)
	{
	  shared_memory[i * 4 + j] = 0;
	}
    }

  pid_t pid = fork ();
  if (pid == 0)			//first child process
    {
      int P = 0;
      printf ("First child process working with row %d\n", P + 1);

      // calculate row 1
      for (int k = 0; k < col; k++)
	{
	  for (int j = 0; j < col; j++)
	    {
	      shared_memory[P * 4 + k] += M[P][j] * N[j][k];	//multiply the numbers then add it to the sum in the product matrix
	    }
	  printf (" %d ", shared_memory[P * 4 + k]);
	}
      printf ("\n");
      exit (0);
    }
  else
    {
      pid_t pid2 = fork ();
      if (pid2 == 0)		//second child process
	{
	  int P = 1;
	  printf ("Second child process working with row %d\n", P + 1);
	  // calculate row 2

	  for (int k = 0; k < col; k++)
	    {
	      for (int j = 0; j < col; j++)
		{
		  shared_memory[P * 4 + k] += M[P][j] * N[j][k];	//multiply the numbers then add it to the sum in the product matrix
		}
	      printf (" %d ", shared_memory[P * 4 + k]);
	    }
	  printf ("\n");
	  exit (0);
	}

      else
	{
	  pid_t pid3 = fork ();
	  if (pid3 == 0)	//third child process
	    {
	      int P = 2;
	      printf ("Third child process working with row %d\n", P + 1);
	      // calculate row 3

	      for (int k = 0; k < col; k++)
		{
		  for (int j = 0; j < col; j++)
		    {
		      shared_memory[P * 4 + k] += M[P][j] * N[j][k];	//multiply the numbers then add it to the sum in the product matrix
		    }
		  printf (" %d ", shared_memory[P * 4 + k]);
		}

	      printf ("\n");
	      exit (0);
	    }
	  else
	    {
	      pid_t pid4 = fork ();
	      if (pid4 == 0)	//fourth child process
		{
		  int P = 3;
		  printf ("Fourth child process working with row %d\n",
			  P + 1);
		  // calculate row 4

		  for (int k = 0; k < col; k++)
		    {
		      for (int j = 0; j < col; j++)
			{
			  shared_memory[P * 4 + k] += M[P][j] * N[j][k];	//multiply the numbers then add it to the sum in the product matrix
			}
		      printf (" %d ", shared_memory[P * 4 + k]);
		    }
		  printf ("\n");
		  exit (0);
		}
	      else
		{
		  while ((wait (&status)) > 0);
		  printf ("\n\n");

		  //print M, N and Q
		  printf ("M is: \n");
		  for (int i = 0; i < 4; i++)
		    {
		      for (int j = 0; j < 4; j++)
			{
			  printf ("%d ", M[i][j]);
			}
		      printf ("\n");
		    }
		  printf ("N is:\n");
		  for (int i = 0; i < 4; i++)
		    {
		      for (int j = 0; j < 4; j++)
			{
			  printf ("%d ", N[i][j]);
			}
		      printf ("\n");
		    }

		  printf ("Q is:\n");
		  for (int i = 0; i < 4; i++)
		    {
		      for (int j = 0; j < 4; j++)
			{
			  printf (" %d ", shared_memory[i * 4 + j]);
			}
		      printf (" \n", shared_memory[i * 4 + j]);
		    }
		  exit (0);
		}
	    }

	}
    }
  exit (0);
  return 0;
}