# include <stdio.h>

int main ( )
{
  int i;
  int j;
  int m;
  int n;

  printf ( "Enter M and N, the matrix dimensions:" );
  scanf ( "%i%i", &m, &n );
//
//  Only declare the matrix at run time, after you have gotten the size.
//
  int a[m][n];
//
//  To make sure this works, let's fill up the matrix with numbers.
//
  for ( i = 0; i < m; i++ )
  {
    for ( j = 0; j < n; j++ )
    {
      a[i][j] = 10 * i + j;
    }
  }
//
//  And now we'll print out our matrix.
//
  for ( i = 0; i < m; i++ )
  {
    for ( j = 0; j < n; j++ )
    {
      printf ( "%4i", a[i][j] );
    }
    printf ( "\n" );
  }

  return 0;
}