This program is to implement dijkstra’s algorithm using colour codes

#include<iostream>
#include<stdlib.h>
#define MAX 20
#define INFINITY 9999
using namespace std;
class dijkstra{
      private:
               int n;
               int graph[MAX][MAX];
               int colour[MAX];
               int start;
               int distance[MAX];
               int predecessor[MAX];
               enum {green,yellow,red};
      public:
             void read_graph();
             void initialize();
             int select_min_distance_lable();
             void update(int);
             void output();
             void function();
      };
void dijkstra::read_graph()
{
     cout<<"Enter the no. of nodes in the graph ::";
     cin>>n;
     cout<<"Enter the adjacency matrix for the graph ::\n";
     int i,j;
     for(i=1;i<=n;i++)
     for(j=1;j<=n;j++)
     cin>>graph[i][j];
     for(i=1;i<=n;i++)
     colour[i]=green;
     cout<<"Enter the start vertex ::";
     cin>>start;
}
void dijkstra::initialize()
{
     for(int i=1;i<=n;i++)
     {
             if(i==start)
             distance[i]=0;
             else
             distance[i]=INFINITY;
             }
     for(int j=1;j<=n;j++)
     {
             if(graph[start][j]!=0)
             predecessor[j]=start;
             else
             predecessor[j]=0;
             }
                              }
int dijkstra::select_min_distance_lable()
{
   
    int min=INFINITY;
    int p=0;
    for(int i=1;i<=n;i++)
                          {
    if(colour[i]==green)
                        {
    if(min>=distance[i])
                        {
                        min=distance[i];
                        p=i;
                        }
                         }
                          }
return p;
}     
void dijkstra::update(int p) // p is a yellow colour node
{
     cout<<"\nupdated distances are ::\n";
     for(int i=1;i<=n;i++)
     {
     if(colour[i]==green)
     {
     if(graph[p][i]!=0)
     {
     if(distance[i]>graph[p][i]+distance[p])
     {
     distance[i]=graph[p][i]+distance[p];
     predecessor[i]=p;
     }
           }
                      }
                      cout<<distance[i]<<'\t';
                      }
                       }
void dijkstra::output()
{
     cout<<"****** The final paths and the distacnes are ******\n\n";
     for(int i=1;i<=n;i++)
     {
         if(predecessor[i]==0 && i!=start)
         {
         cout<<"path does not exists between "<<i<<" and the start vertex "<<start<<endl;
         exit(1);
         }
         cout<<"path for node “<<i<<” is ::\n";
         int j=i;
         int array[MAX];
         int l=0;
         while(predecessor[j]!=0)
         {
         array[++l]=predecessor[j];
         j=predecessor[j];
         }
         for(int k=l;k>=1;k=-k)
         cout<<array[k]<<"->";
         cout<<i<<endl;
         cout<<"distance is "<<distance[i]<<endl<<endl<<endl;
         }
         }

void dijkstra::function()
{
    
     cout<<"\n**********************************************************************\n";
     cout<<"This program is to implement dijkstra’s algorithm using colour codes \n";
     cout<<"**********************************************************************\n\n";
     read_graph();
     initialize();
     //repeate until all nodes become red
     int flag=0;
     int i;
     cout<<"\n\n******** The working of the algorithm is **********\n\n";
     for(i=1;i<=n;i++)
     if(colour[i]!=red)
     flag=1;
     cout<<"The initial distances are ::\n";
     for(i=1;i<=n;i++)
     cout<<distance[i]<<'\t';
     cout<<endl;
     while(flag)
                {
                int p=select_min_distance_lable();
                cout<<"\nThe min distance lable that is coloured yellow is "<<p;
                colour[p]=yellow;
                update(p);
                cout<<"\nnode "<<p<<" is coloured red "<<endl;
                colour[p]=red;
                flag=0;
                for(i=1;i<=n;i++)
                if(colour[i]!=red)
                flag=1;
                cout<<endl<<endl<<endl;
                }
                output();
}

int main()
{
dijkstra d;
d.function();
}