Topological Sort using DFS

#include <iostream>
#include <list>

using namespace std;

int v,t;
int matrix[100][100];
int clr[100], dis[100], fin[100], prev[100];
int t_edge,b_edge,f_edge,c_edge;

list <int> tp_sort;
list <int> :: iterator it;

void DFS();
void DFS_visit(int s);

int main ()
{
    int  r, c, n, s;
    int edge = 1;

    cout<<"Input no of vertices: ";
    cin>>v;

    do{
        cout<<"Edge "<<edge<<": ";
        cin>>r>>c;
         if(r>v || c>v)
            cout<<"Invalid input"<<endl;
        else{
            matrix[r][c] = 1;
            edge++;
        }
    }while(r != 0 && c!=0);

    DFS();

    if(b_edge > 0)
        cout<<endl<<"Topological sort can't be determined!!!(Cyclic Graph)"<<endl;
    else{
        cout<<endl<<endl<<"Topological sort : ";
        for(it = tp_sort.begin(); it != tp_sort.end(); it++)
            cout<< *it << " ";
    }

    cout<<endl;

    return 0;
}

void DFS ()
{
    int i;
    t =0;
    t_edge = 0;
    b_edge = 0;
    f_edge = 0;
    c_edge = 0;

    for(i=0; i<=v; i++)
    {
        clr[i] = 0;
        dis[i] = 2000000;
        fin[i] = 2000000;
        prev[i] = -1;
    }

    for(i=1; i<=v; i++)
    {
        if(clr[i] == 0)
            DFS_visit(i);
    }

    //printing
    cout<<endl<<"vertex : ";
    for(i=1; i<=v; i++)
        cout<<i<<"   ";

    cout<<endl<<"d[u]   : ";
    for(i=1; i<=v; i++)
        cout<<dis[i]<<"   ";

    cout<<endl<<"f[u]   : ";
    for(i=1; i<=v; i++)
        cout<<fin[i]<<"  ";

    //edges
    cout<<endl<<"No of tree edge: "<< t_edge;
    cout<<endl<<"No of back edge: "<< b_edge;
    cout<<endl<<"No of forward edge: "<< f_edge;
    cout<<endl<<"No of cross edge: "<< c_edge;
}

void DFS_visit(int s)
{
    int i;

    clr[s] = 1;
    dis[s] = ++t;

    for(i=1; i<=v; i++)
    {
        if(matrix[s][i] == 1 && clr[i] == 2)
        {
            if (dis[s] < dis[i]){
                    f_edge++;
                cout<<s<<"-"<<i<<" : Forward Edge"<<endl;
            }
            else{
                    c_edge++;
                cout<<s<<"-"<<i<<" : Cross Edge"<<endl;
            }
        }
        else if(matrix[s][i] == 1 && clr[i] == 1){
                b_edge++;
            cout<<s<<"-"<<i<<" : Back Edge"<<endl;
        }
        else
        {
            if(matrix[s][i] == 1 && clr[i] == 0)
            {
                prev[i] = s;
                cout<<s<<"-"<<i<<" : Tree Edge"<<endl;
                t_edge++;
                DFS_visit(i);
            }
        }
    }
    clr[s] = 2;
    fin[s] = ++t;
    tp_sort.push_front(s);

}