taking input from a file (graph)

[valiciousx]

Hi,

So I need to represent a graph using adjacency matrix.The number of vertices and edges I have to read them from a file data.txt
Here is the file

6 9 // 6= nr of vertices; 9=nr of edges
1 2 2 // edge 1 edge 2 cost
1 3 4 // edge 1 edge 3 cost
2 3 1 // edge 2 edge 3 cost
2 4 4
2 5 2
3 5 3
4 6 2
5 4 3
5 6 2

5 7 // 5= nr of vertices; 7=nr of edges
1 2 10
1 4 30
1 5 100
2 3 50
3 5 10
4 3 20
4 5 60

Here is my code.

  #include <iostream>
#include <fstream>
using namespace std;


int main() {
  ifstream infile("data.txt");
  int n,m;
  int a,b,c;
  int cost[100][100];
  for(int i=0;i<n;++i) {
    for(int j=0;j<n;++j) {
      cost[i][j]=0;
    }
  }
  if (infile>>n>>m) {
    while (infile>>a>>b>>c) {
      for(int i=0;i<n;++i) {
        for(int j=0;j<n;++j) {
          cost[a-1][b-1]=c;
        }
      }
    }
  }
  for(int i=0;i<n;++i) {
    for(int j=0;j<n;++j) {
      cout<<cost[i][j]<<" ";
    }
    cout<<endl;
  }
  infile.close();
}

The problem is that my code prints the matrix just for the first set of data.What I have to do such that the program prints the second matrix?

[MikeyBoy]

A simple loop would work. Keep looping until the of the file is reached.

For good, readable program structure, I'd advise putting all the code that reads a single matrix into a function, and then call that function on each iteration of the loop.

[lastchance]

Are you sure that your graph isn't undirected?

Your data seems to correspond to TWO graphs?

#include <iostream>
#include <iomanip>
#include <sstream>
#include <vector>
using namespace std;

class Graph
{
   int numVert;
   vector< vector<int> > adj;

public:
   Graph( istream &in  );
   void write( ostream &out );
};

Graph::Graph( istream &in )
{
   int nedge, a, b, cost;
   in >> numVert >> nedge;
   adj = vector< vector<int> >( numVert, vector<int>( numVert, 0 ) );
   for ( int i = 0; i < nedge; i++ )
   {
      in >> a >> b >> cost;
      adj[a-1][b-1] = cost;
//    adj[b-1][a-1] = cost;            // need this as well if graph is undirected
   }
}

void Graph::write( ostream &out )
{
   for ( int i = 0; i < numVert; i++ )
   {
      for ( int j = 0; j < numVert; j++ ) out << setw( 2 ) << adj[i][j] << ' ';
      out << '\n';
   }
}

//======================================================================

int main()
{
   istringstream in( "6 9    \n"
                     "1 2 2  \n"
                     "1 3 4  \n"
                     "2 3 1  \n"
                     "2 4 4  \n"
                     "2 5 2  \n"
                     "3 5 3  \n"
                     "4 6 2  \n"
                     "5 4 3  \n"
                     "5 6 2  \n"
                     "       \n"
                     "5 7    \n"
                     "1 2 10 \n"
                     "1 4 30 \n"
                     "1 5 100\n"
                     "2 3 50 \n"
                     "3 5 10 \n"
                     "4 3 20 \n"
                     "4 5 60 \n" );

   Graph G(in), H(in);

   G.write( cout );
   cout << "\n\n";
   H.write( cout );
}

 0  2  4  0  0  0 
 0  0  1  4  2  0 
 0  0  0  0  3  0 
 0  0  0  0  0  2 
 0  0  0  3  0  2 
 0  0  0  0  0  0 


 0 10  0 30 100 
 0  0 50  0  0 
 0  0  0  0 10 
 0  0 20  0 60 
 0  0  0  0  0