Having some problems with binary search can someone look to it?

Question

Binary search and bubblesort problem. Cant understand the problem with binary search pseudocode.What do i need to change in order to get the index of targeted number?

import java.util.*;
public class Binarysearch2 {
    
    static void bubblesort(int dizi[]){  // bubblesort //
        int o,p,temp;
        for(o=0;o<dizi.length-1;o++)
        {
            for(p=0;p<dizi.length-1-o;p++)
            {
                if(dizi[p+1]>dizi[p]){
                    temp=dizi[p];
                    dizi[p]=dizi[p+1];
                    dizi[p+1]=temp;
                }
            }
        }
    }
    
    static int search(int dizi[],int aranan) // binary search//
    {
        int ust=dizi.length-1;
        int alt=0;
        
        while(alt<=ust)
        {
            int orta=(alt+ust)/2;
            if(dizi[orta]==aranan){
                return orta;
            }
            else if (orta<aranan)
            {
                alt=orta+1;
            }
            else
                ust=orta-1;
        }
        return -1;
    }

public static void main(String[]args) //main//
{
Scanner tara=new Scanner(System.in);
System.out.println("Enter array lenght");
int x=tara.nextInt();
Random rnd= new Random();
int i;
int a[]=new int[x];
for(i=0;i<x;i++)
{
 a[i]=(1+rnd.nextInt(6));
System.out.print(a[i]+" ");

}
System.out.println();
System.out.println("Enter targeted number :");
int k,z;
k=tara.nextInt();
bubblesort(a);

z=Binarysearch2.search(a,k);

if(z==-1)
{System.out.println("Target is not in array.");}
else 
    System.out.println(k+" in array "+z +" . at this index.");

}}

i think something in binarysearch is wrong.

Answer 1

Good day, It would be really helpful if you'll be using english to name variables. Binary search making an important assumption, that array, where you are seeking for an element, has been sorted. So, if you would add sorting into search method as such, your code will work:

    static int search(int dizi[], int aranan) {
        int ust = dizi.length - 1;
        int alt = 0;

        Arrays.sort(dizi); // ADDED ELEMENT

        while (alt <= ust) {
            int orta = (alt + ust) / 2;
            if (dizi[orta] == aranan) {
                return orta;
            } else if (orta < aranan) {
                alt = orta + 1;
            } else
                ust = orta - 1;
        }
        return -1;
    }

Answer 2

There's a problem here:

if (orta<aranan)
{
    alt=orta+1;
}

Instead of comparing the value (dizi[orta]) to the target (aranan), you're comparing the index. Just replace the condition with if (dizi[orta]<aranan)

Also, as Anatoly points out correctly in his answer, you're sorting in the wrong direction. Your bubble sort swaps elements when the lower one is smaller than the bigger one (if(dizi[p+1]>dizi[p]) . That means that you're sorting in descending order. On the other hand, your search assumes that the array is sorted in ascending order.

Answer 3

1. Array sorting in wrong direction. In bubblesort change dizi[p+1] > dizi[p] on dizi[p+1] < dizi[p]
2. In search change else if (orta < aranan) on else if (dizi[orta] < aranan)