How Multithreading in c++ is done

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C++/CLI

multi-threading

Hi!
I have design one c++ multithreading application (first time) in which one thread does following task: it read values from file & insert into dynamic queue. Second thread does read values from queue and write into output file; Sometimes task is done as i wish like 'Queue is write complete'(output of first thread) and after 'Queue read completed'(output of second thread),but sometimes it behaves abnormal means it shows output of second thread & then output of first thread;also sometimes output of first thread,not second and wiseversa.
Below i copied my code,please suggest any changes required for it.
Also my doubt:Is that operating system monitors these threads,so it shows different output?

#include <iostream>
using namespace std;
#include<windows.h>
const int MAX = 2*1048576;
int Size ;
HANDLE hThread1,hThread2;
DWORD dwID1,dwID2;
DWORD Thread1(LPVOID param);
DWORD Thread2(LPVOID param);
FILE *fp,*fpOut;
  class cqueue
  {
	 
	public :
		static int front,rear;
		static int *a;//=new int[1048576];
	   cqueue()
	   {
		 front=rear=-1;
		 a=new int[MAX];
	   }
	   ~cqueue()
	   {
		delete[] a;
	   }
	  
	  static void insertWithAck(char);
	  static int deletionWithAck();
  };

int cqueue::front;
int cqueue::rear;
int* cqueue::a;

void cqueue :: insertWithAck(char val)
{
 while((rear==MAX-1) || (rear+1==front)) ;
   if(rear==MAX-1)
	  rear=0;
   else	
	 rear++;
   a[rear]=val;
 if(front==-1)
   front=0;
}

int cqueue :: deletionWithAck()
{
 char k;
 while(front== -1);
	
	k=a[front];
	if(front==rear)
	   front=rear=-1;
	else
	{
	   if(front==MAX-1)
		  front=0;
	   else
		  front++;
	}
 
 return k;
}
DWORD Thread1(LPVOID param)
{
	int i,val;

	fp=fopen("1MB_TEST_FILE.txt","rb");
	fseek(fp,0,SEEK_END);
	Size=ftell(fp);
	rewind(fp);
	for(i=0;i<Size;i++){
			fread(&val,1,1,fp);
			cqueue::insertWithAck(val);
	}
	fclose(fp);
	cout<<"Queue write completed\n";   
   return 0;
}
DWORD Thread2(LPVOID param)
{	
	fpOut=fopen("OutFile.txt","wb");
	char retVal;
	
	for(int i=0;i<Size;i++){
		retVal=cqueue::deletionWithAck();
		fwrite(&retVal,1,1,fpOut);
	}
	fclose(fpOut);
	cout<<"Queue read completed\n";
	return 0;
}

void main()
{
	 cqueue c1;
	 hThread1= CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)Thread1,NULL,0,&dwID1);
	
	 hThread2= CreateThread(NULL,0,(LPTHREAD_START_ROUTINE)Thread2,NULL,0,&dwID2);
system("pause")
}