Topological sorting program in c++

 Topological sorting program in c++

#include <iostream>

using namespace std;

#define MAX 100

int n; /*Number of vertices in the graph*/

int adj[MAX][MAX]; /*Adjacency Matrix*/

void create_graph();

int queue[MAX], front = -1,rear = -1;

void insert_queue(int v);

int delete_queue();

int isEmpty_queue();

int indegree(int v);

int main()

{

    int i,v,count,topo_order[MAX],indeg[MAX];

    create_graph();

    /*Find the indegree of each vertex*/

    for(i=0; i<n; i++)

    {

        indeg[i] = indegree(i);

        if( indeg[i] == 0 )

            insert_queue(i);

    }

    count = 0;

    while( !isEmpty_queue( ) && count < n )

    {

        v = delete_queue();

        topo_order[++count] = v; /*Add vertex v to topo_order array*/

        /*Delete all edges going fron vertex v */

        for(i=0; i<n; i++)

        {

            if(adj[v][i] == 1)

            {

                adj[v][i] = 0;

                indeg[i] = indeg[i]-1;

                if(indeg[i] == 0)

                    insert_queue(i);

            }

        }

    }

    if( count < n )

    {

        cout<<("\nNo topological ordering possible, graph contains cycle\n");

        exit(1);

    }

    cout<<("\nVertices in topological order are :\n");

    for(i=1; i<=count; i++)

        cout<<( topo_order[i] );

    cout<<("\n");

    return 0;

}/*End of main()*/

void insert_queue(int vertex)

{

    if (rear == MAX-1)

        cout<<("\nQueue Overflow\n");

    else

    {

        if (front == -1) /*If queue is initially empty */

            front = 0;

        rear = rear+1;

        queue[rear] = vertex ;

    }

}/*End of insert_queue()*/

int isEmpty_queue()

{

    if(front == -1 || front > rear )

        return 1;

    else

        return 0;

}/*End of isEmpty_queue()*/

int delete_queue()

{

    int del_item;

    if (front == -1 || front > rear)

    {

        cout<<("\nQueue Underflow\n");

        exit(1);

    }

    else

    {

        del_item = queue[front];

        front = front+1;

        return del_item;

    }

}/*End of delete_queue() */

int indegree(int v)

{

    int i,in_deg = 0;

    for(i=0; i<n; i++)

        if(adj[i][v] == 1)

            in_deg++;

    return in_deg;

}/*End of indegree() */

void create_graph()

{

    int i,max_edges,origin,destin;

    cout<<("\nEnter number of vertices : ");

    cin>>(n);

    max_edges = n*(n-1);

    for(i=1; i<=max_edges; i++)

    {

        cout<<"\nEnter edge (-1 -1 to quit)"<<i<<":";

        cin>>origin;
        cin>>destin;

        if((origin == -1) && (destin == -1))

            break;

        if( origin >= n || destin >= n || origin<0 || destin<0)

        {

            cout<<("\nInvalid edge!\n");

            i--;

        }

        else

            adj[origin][destin] = 1;

    }

}