Binary Search

[noysoffer]

Hi,
I tried to write a binary search algorithm, but for some reason, I have an error:

// Search.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"
#include <iostream>
#include <stdlib.h>
using namespace std;

void generate_sorted_array(int n, int* &arr)
{
	arr=new int[n];
		
	for (int i=0; i<n; ++i)
	{
		arr[i]=i;
	}
}

int search_x(int x, int* arr, int n)
{
	int start=0;
	int size=n;

	while(size!=0)
	{
		int mid=start+size/2;
		if (x>arr[mid])
		{
			start=mid+1;
			size=size/2;
		}

		else if (x<arr[mid])
		{
			size=size/2;
		}

		else 
			return mid;
	}
	return -1;
}

void print_array(int n, int* arr)
{
	for (int i=0; i<n; ++i);
	{
		cout << arr[i] << ",";
	}
}

void main()
{
	int* arr;
	generate_sorted_array(100, arr);
	print_array(100,arr);

	int found_number=search_x(0,arr,100);
	cout << found_number << endl;
}

But I have an error at the:

for (int i=0; i<n; ++i);
	{
		cout << arr[i] << ",";
	}

The error is that i isn't defined apparently. But I don't understand why.

Thanks a lot for the help. :)

[Peter87]

Remove the semicolon at the end of line 46.

[noysoffer]

I did that, and I still have the same error.

[Akshit]

Removing ; should work.Check properly or see the revised code

#include <iostream>
#include <stdlib.h>
using namespace std;

void generate_sorted_array(int n, int* &arr)
{
	arr=new int[n];
		
	for (int i=0; i<n; ++i)
	{
		arr[i]=i;
	}
}

int search_x(int x, int* arr, int n)
{
	int start=0;
	int size=n;

	while(size!=0)
	{
		int mid=start+size/2;
		if (x>arr[mid])
		{
			start=mid+1;
			size=size/2;
		}

		else if (x<arr[mid])
		{
			size=size/2;
		}

		else 
			return mid;
	}
	return -1;
}

void print_array(int n, int* arr)
{
	for (int i=0; i<n; ++i)
	{
		cout << arr[i] << ",";
	}
}

void main()
{
	int* arr;
	generate_sorted_array(100, arr);
	print_array(100,arr);

	int found_number=search_x(5,arr,100);
	cout << endl << found_number << endl;
	cin.get();
}

[georgep]

You should not be using void main(). Main should always ALWAYS ALWAYS return an int.

[TheIdeasMan]

I am using g++ 4.7.1 with c++11 enabled and I have trouble with this:

for (int i=0; i<n; ++i)

doing this fixes it:

int i;
for (i=0; i<n; ++i)

Maybe this is your problem too?

I am not sure why I have this problem, I thought the first syntax had been around for a while.

HTH

[noysoffer]

I'm not having this problem. When I wrote int i, there was an error that i was defined before being initialized. I actually tried to fix the code with the comments written here, and I still had the same error. Apparently, there's a system error, not a code error. I sent the code to a friend, who ran the code on his computer, and he didn't have any problems, despite the fact that he didn't change the code at all.

[Peter87]

Make sure that the code that you see is the code that you compile and run. Not some copy of it.

[TheIdeasMan]

When I wrote int i, there was an error that i was defined before being initialized.

Maybe this following code is a bit pedantic, but it should always work. I would be upset if it doesn't because that is C style that has been around forever.

int i = 0;  //declare and initialise
for (i=0; i<n; ++i)  //notice dont specify int again 

Maybe you should post the exact compiler output?

I sent the code to a friend, who ran the code on his computer, and he didn't have any problems, despite the fact that he didn't change the code at all.

That implies different compiler settings - a system error as you say. We would need to know lots about your system to fix that. The compiler & version, the compiler flags, maybe the compile command being used. Some of this we could see from the compiler output.