#include <stdio.h>
#include <limits.h>

#define MaxSize 10
#define Infinity 1000
int w[ MaxSize ][ MaxSize ], v[ MaxSize ], e1, e2, n, s;


void main()
{
   int i, j, k, a, b, c, min, add_vertex;

   printf( "Enter n: " );
   scanf( "%d", &n );

   for ( i = 1; i <= n; i++ )
      for ( j = 1; j <= n; j++ )
         w[ i ][ j ] = Infinity;

   for ( ; ; ) {
      printf( "Enter edge (i,j) and weight\n"
              "Negative to quit: " );
      scanf( "%d%d%d", &a, &b, &c );
      if ( a < 0 || b < 0 || c < 0 )
         break;
      w[ a ][ b ] = w[ b ][ a ] = c;
   }

   printf( "Enter start vertex: " );
   scanf( "%d", &s );
   printf( "\nBeginning Prim's algor\n\n" );

   for ( i = 1; i <= n; i++ )
      v[ i ] = 0;
   v[ s ] = 1;
   for ( i = 1; i <= n - 1; i++ ) {
      min = Infinity;
      for ( j = 1; j <= n; j++ )
         if ( v[ j ] == 1 )
            for ( k = 1; k <= n; k++ )
               if ( v[ k ] == 0 && w[ j ][ k ] < min ) {
                  printf( "Examining edge (%d,%d)\n", j, k );
                  add_vertex = k;
                  e1 = j;
                  e2 = k;
                  min = w[ j ][ k ];
               }
      v[ add_vertex ] = 1;
      printf( "Adding edge (%d,%d)\n\n", e1, e2 );
   }
}