Bfs Dfs (java)

package bfsdfs;

import java.util.Scanner;

public class Main
{
    static int top=-1,front=-1,rear=-1;
    static int[][] a=new int[20][20];
    static int[] q=new int[20];
    static int[] stack=new int[20];
    static int[] vis = new int[20];

    static void bfs(int s,int n)
    {
        int p,i;
        add(s);
        vis[s]=1;
        p=delete();
        if(p!=0)
            System.out.format(" %d",p);
        while(p!=0)
        {
            for(i=1; i<=n; i++)
                if((a[p][i]!=0)&&(vis[i]==0))
                {
                    add(i);
                    vis[i]=1;
                }
            p=delete();
            if(p!=0)
                System.out.format(" %d ",p);
        }
        for(i=1; i<=n; i++)
            if(vis[i]==0)
                bfs(i,n);
    }


    static void add(int item)
    {
        if(rear==19)
            System.out.format("QUEUE FULL");
        else
        {
            if(rear==-1)
            {
                q[++rear]=item;
                front++;
            }
            else
                q[++rear]=item;
        }
    }
    static int delete()
    {
        int k;
        if((front>rear)||(front==-1))
            return(0);
        else
        {
            k=q[front++];
            return(k);
        }
    }


//***************DFS(depth-first search) code******************//
    static void dfs(int s,int n)
    {
        int i,k;
        push(s);
        vis[s]=1;
        k=pop();
        if(k!=0)
            System.out.format(" %d ",k);
        while(k!=0)
        {
            for(i=1; i<=n; i++)
                if((a[k][i]!=0)&&(vis[i]==0))
                {
                    push(i);
                    vis[i]=1;
                }
            k=pop();
            if(k!=0)
                System.out.format(" %d ",k);
        }
        for(i=1; i<=n; i++)
            if(vis[i]==0)
                dfs(i,n);
    }
    static void push(int item)
    {
        if(top==19)
            System.out.format("Stack overflow ");
        else
            stack[++top]=item;
    }
    static int pop()
    {
        int k;
        if(top==-1)
            return(0);
        else
        {
            k=stack[top--];
            return(k);
        }
    }

    public static void main(String[] args)
    {
        Scanner scanner = new Scanner(System.in);
        int n,i,s,ch,j;
        char c,dummy;
        System.out.format("\nENTER THE NUMBER VERTICES : ");

        n = scanner.nextInt();
        for(i=1; i<=n; i++)
        {
            for(j=1; j<=n; j++)
            {
                System.out.format("ENTER 1 IF %d HAS A NODE WITH %d ELSE 0 : ",i,j);

                a[i][j] = scanner.nextInt();
            }
        }
        System.out.format("THE ADJACENCY MATRIX IS\n");
        for(i=1; i<=n; i++)
        {
            for(j=1; j<=n; j++)
            {
                System.out.format(" %d",a[i][j]);
            }
            System.out.format("\n");
        }

        do
        {
            for(i=1; i<=n; i++)
                vis[i]=0;
            System.out.format("\nMENU");
            System.out.format("\n1.B.F.S");
            System.out.format("\n2.D.F.S");
            System.out.format("\nENTER YOUR CHOICE : ");
            ch = scanner.nextInt();

            System.out.format("ENTER THE SOURCE VERTEX : ");
            s = scanner.nextInt();

            switch(ch)
            {
            case 1:
                bfs(s,n);
                break;
            case 2:
                dfs(s,n);
                break;
            }
            System.out.format("\nDO U WANT TO CONTINUE(Y/N) ? ");
            c = scanner.next().charAt(0);
        }
        while((c=='y')||(c=='Y'));
    }
}