**fig9_7.txt**

/* 1*/	void
/* 2*/	Topsort( Graph G )
/* 3*/	{
/* 4*/	    unsigned int Counter = 1;
/* 5*/	    Vertex V, W;
/* 6*/	    Queue<Vertex> Q( Num_Vertex );

/* 7*/	    for Each Vertex V
/* 8*/	        if( Indegree[ V ] == 0 )
/* 9*/	            Q.Enqueue( V );

/*10*/	    while( !Q.Is_Empty( ) )
/*11*/	    {
/*12*/	        V = Q.Dequeue( );
/*13*/	        Top_Num[ V ] = Counter++;

/*14*/	        for Each W Adjacent To V
/*15*/	            if( --Indegree[ W ] == 0 )
/*16*/	                Q.Enqueue( W );
/*17*/	    }

/*18*/	    if( Counter <= Num_Vertex )
/*19*/	        Error( "Graph has a cycle" );
/*20*/	}