Binary search of a sorted array error

Question

using System.IO;
using System;
class Class1
{
    static void Main(string[] args)
    {
        int[] arr = new int[10] { 1,3,2,4,5,7,6,8,10,9};
        int l = 1, r = 10, m = 0,t;

        sort(arr, 10); 
        int i;
        for (i = 0; i < 10; i++)
        {
            Console.Write(arr[i] + "\t");
        }
        Console.WriteLine("Please entert the number");
        t = Convert.ToInt32(Console.ReadLine());

        m = (l + r) / 2;

        while(l>=r)
        {
            if (arr[m] == t)
               Console.WriteLine("value is : " + m);
            if (arr[m] < t)
                l = m + 1;
            if (arr[m] > t)
                r = m - 1;
            else
                Console.WriteLine("Target was found at index  " + arr[m]);
        }
    }

    static void sort(int[] dataset, int n)
    {
        int i, j;
        for (i = 0; i < n; i++)
            for (j = n - 1; j > i; j--)
                if (dataset[j] < dataset[j - 1])
                {
                    int temp = dataset[j];
                    dataset[j] = dataset[j - 1];
                    dataset[j - 1] = temp;
                }
    }
}

I tried running this program. I got output as :

sh-4.3$ mcs *.cs -out:main.exe
sh-4.3$ mono main.exe
1 2 3 4 5 6 7 8 9
10
Please enter the number
5
sh-4.3$

What should I do to get the output of binary search from the sorted array?

You know you could use Array.Sort instead of writing your own bubble sort implementation. — juharr
– juharr, Commented Apr 6, 2016 at 11:46
You do realize that l is never >= r. So you never enter the while loop. I think you want while(l<=r) — juharr
– juharr, Commented Apr 6, 2016 at 11:47
thanks for the info @juharr. but i wanted to try it with bubble sort. is there an error in my code? — Phoenix.1993
– Phoenix.1993, Commented Apr 6, 2016 at 11:49
Also your else in the while loop will never be reached since arr[m] can only be equal to, less than, or greater than t. There are no other possibilities. — juharr
– juharr, Commented Apr 6, 2016 at 11:53

Vikhram · Accepted Answer · 2016-04-06 11:53:35Z

1

There are lots of issues with your code

Bad formatting - make it difficult to read
Bad variable names - make it difficult to understand
Variables not declared close to where they are being used
Not using inbuilt routine for sort (assuming your focus is on learning binary search)

Now, logically the code fails, since the while loop for your binary search is flawed. Below is the correct code for your main - I have tried to keep it as similar to your code as possible, so you can understand the issues

static void Main(string[] args) {
    int[] arr = new int[10] { 1, 3, 2, 4, 5, 7, 6, 8, 10, 9 };


    sort(arr, 10);
    int i;
    for (i = 0; i < 10; i++) {
        Console.Write(arr[i] + "\t");
    }

    int t;
    Console.WriteLine("Please entert the number");
    t = Convert.ToInt32(Console.ReadLine());

    bool found = false;
    int l = 0, r = arr.Length - 1, m = 0;
    while (!found && l <= r) {
        m = (l + r) / 2;
        if (arr[m] == t)
            found = true;
        else if (arr[m] < t)
            l = m + 1;
        else if (arr[m] > t)
            r = m - 1;
    }
    if (found)
        Console.WriteLine($"value {t} is located at index {m}");
    else
        Console.WriteLine($"value {t} not found");
}

answered Apr 6, 2016 at 11:53

Vikhram

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3 Comments

Phoenix.1993 Over a year ago

thank you for your effort and help. i am a fresher in C# and in learning process... Sorry for the trouble..... Thanks again!

Phoenix.1993 Over a year ago

btw. Console.WriteLine($"value {t} is located at index {m}"); What is the necessity of $ and {} in that statement?

Vikhram Over a year ago

It is a new syntax with c# 6. In older versions, you can write that as Console.WriteLine("value {0} is located at index {1}", t, m). Read up on Interpolated strings for more details

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