L-36 MCS 260 Mon 12 Nov 2001

/* L-36 MCS 260 Mon 12 Nov 2001 : floating-point matrices 

In this program we consider a floating-point matrix to store
information about terrain heights.  Imagine we place an n-by-m 
grid on a terrain.  At each grid point, we measure the elevation.

Observe the following :

  1) We use an intermediate function heights to achieve
     the flexibility of variable dimensions of the matrix.

  2) If we use arrays of variable dimensions in functions,
     then we must pass the number of rows and columns.

  3) In the function to find the peak, we initialize the maximum
     as the first element in the matrix.                       */

#include<stdio.h>

/* we use the following function to allow the user to use any
   number of rows and columns in the matrix :                  */

void heights ( int n, int m );
/* declares an n-by-m matrix of floating-point entries, reads in
   the entries, looks for the highest peak  */

int main ( void )
{
   int rows,cols;

   printf("Give number of rows : "); scanf("%d", &rows);
   printf("Give number of columns : "); scanf("%d", &cols);

   heights(rows,cols);

   return 0;
}

/* all functions are local to the heights function and will not
   be used in the main program, therefore we declare them as static : */

static void read ( int n, int m, float a[n][m] )
/* asks the user to provide the entries of an n-by-m floating matrix */
{
   int i,j;

   printf("Give entries of %d-by-%d matrix :\n", n, m);
   for (i=0; i<n; i++)
      for (j=0; j<m; j++)
         scanf("%f", &a[i][j]);
}

static void write ( int n, int m, float a[n][m] )
/* writes the entries of an n-by-m floating matrix to the screen */
{
   int i,j;

   printf("The entries of a %d-by-%d matrix :\n", n, m);
   for (i=0; i<n; i++)
   {
      for (j=0; j<m; j++)
         printf("  %f", a[i][j]);
      printf("\n");
   }
}

static float average ( int n, int m, float a[n][m] )
/* returns the average height of the terrain */
{
   float sum = 0.0;

   int i,j;

   for (i=0; i<n; i++)
      for (j=0; j<m; j++)
         sum += a[i][j];

   return (sum/(n*m));
}

static float peak ( int n, int m, float a[n][m], int *prow, int *pcol )
/* returns the maximal element in the n-by-m matrix a,
   the coordinates of the maximum are in *prow and *pcol */
{
   float max = a[0][0];
   int i,j;

   *prow = 0;
   *pcol = 0;

   for (i=0; i<n; i++)
      for (j=0; j<m; j++)
         if (a[i][j] > max)
         {
            max = a[i][j];
            *prow = i;
            *pcol = j;
         }

   return max;
}

void heights ( int n, int m )
{
   float h[n][m],p;
   int pr,pc;

   read(n,m,h);
   write(n,m,h);

   printf("The average height : %f\n", average(n,m,h));

   p = peak(n,m,h,&pr,&pc);
   printf("The peak is %f at (%d,%d).\n", p, pr, pc);
}