Многопоточность (вычисление корня квадратного уравнения, используя несколько независимых потоков)

#include<iostream>
#include<windows.h>
#include<process.h>
 
HANDLE hReadPipe, hWritePipe, hSemaphore;
DWORD buf;
 
void f(void* p){
    int num=*reinterpret_cast<int*>(p);
    num*=2;
    if(!WriteFile(hWritePipe, &num, sizeof(num), &buf, NULL)){std::cerr<<"Error writing\n";}
    ReleaseSemaphore(hSemaphore, 1, NULL);
}
 
int main() {
    int num;
    std::cin>>num;
    if(!(hSemaphore=CreateSemaphore(NULL, 0, 1, NULL))){std::cerr<<"Create semaphore error\n"; return GetLastError();}
    if(!CreatePipe(&hReadPipe, &hWritePipe, NULL, 0)){std::cerr<<"Failed pipe creating\n"; return GetLastError();}
    _beginthread(f, 0, &num);
    while(true){
        if(WaitForSingleObject(hSemaphore, 0)==WAIT_OBJECT_0) break;
    }
    ReadFile(hReadPipe, &num, sizeof(num), &buf, NULL);
    std::cout<<num<<"\n";
}

#include<iostream>
#include<windows.h>
#include<process.h>
#include<math.h>
 
HANDLE hReadPipe, hWritePipe, hSemaphore;
DWORD buf, as;
using namespace std;
 
struct oper
{
    int x;
    int y;
};
DWORD WINAPI um (void* p)
{
    oper arg = *reinterpret_cast<oper*>(p);
    int num = arg.x * arg.y;
    if (!WriteFile(hWritePipe, &num, sizeof(num), &buf, NULL))
    {
        cerr<<"Error writing\n";
    }
        ReleaseSemaphore(hSemaphore, 1, NULL);
    ExitThread(0);
    return 0;
} 
DWORD WINAPI plus (void* p)
{
    oper arg = *reinterpret_cast<oper*>(p);
    int num = arg.x + arg.y;
    if (!WriteFile(hWritePipe, &num, sizeof(num), &buf, NULL))
    {
        cerr<<"Error writing\n";
    }
        ReleaseSemaphore(hSemaphore, 1, NULL);
    ExitThread(0);
    return 0;
} 
DWORD WINAPI minus (void* p)
{
    oper arg = *reinterpret_cast<oper*>(p);
    int num = arg.x - arg.y;
    if (!WriteFile(hWritePipe, &num, sizeof(num), &buf, NULL))
    {
        cerr<<"Error writing\n";
    }
        ReleaseSemaphore(hSemaphore, 1, NULL);
    ExitThread(0);
    return 0;
} 
DWORD WINAPI del (void* p)
{
    oper arg = *reinterpret_cast<oper*>(p);
    int num = arg.x/arg.y;
    if (!WriteFile(hWritePipe, &num, sizeof(num), &buf, NULL))
    {
        cerr<<"Error writing\n";
    }
    ReleaseSemaphore(hSemaphore, 1, NULL);
    ExitThread(0);
    return 0;
} 
DWORD WINAPI kor (void* p)
{
    oper arg = *reinterpret_cast<oper*>(p);
    int num = sqrt((double)arg.x);
    if (!WriteFile(hWritePipe, &num, sizeof(num), &buf, NULL))
    {
        cerr<<"Error writing\n";
    }
    ReleaseSemaphore(hSemaphore, 1, NULL);
    ExitThread(0);
    return 0;
} 
int main() 
{
    int a,b,c,res2,res1,res3,x1,x2;
    cout<<"a = ";
        cin>>a;
    cout<<"b = ";
        cin>>b;
    cout<<"c = ";
        cin>>c;
    if (!(hSemaphore=CreateSemaphore(NULL, 0, 1, NULL)))
    {
        cerr<<"Create semaphore error\n"; 
        return GetLastError();
    }
    if (!CreatePipe(&hReadPipe, &hWritePipe, NULL, 0))
    {
        cerr<<"Failed pipe creating\n"; 
        return GetLastError();
    }
    oper arg; 
    ////////////////Умножаем 4 и а//////////////////////////////////////////
    arg.x = a;
    arg.y = 4;
    CreateThread(NULL, 0, um, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res2, sizeof(res2), &buf, NULL);
//  cout<<"4a="<<res2<<"\n";
    ////////////////Умножаем 4а и с////////////////////////////////////////
    arg.x = res2;
    arg.y = c;
    CreateThread(NULL, 0, um, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res2, sizeof(res2), &buf, NULL);
//  cout<<"4ac="<<res2<<"\n";
    ////////////////Возводим b в квадрат//////////////////////////////////
    arg.x = b;
    arg.y = b;
    CreateThread(NULL, 0, um, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res1, sizeof(res1), &buf, NULL);
//  cout<<"b2="<<res1<<"\n";
    ////////////////Вычисляем дискриминант по формуле b^2 - 4ac///////////////
    arg.x = res1;
    arg.y = res2;
    CreateThread(NULL, 0, minus, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res1, sizeof(res1), &buf, NULL);
//  cout<<"D="<<res1<<"\n";
    arg.x = res1;
    arg.y = 0;
    ////////////////Проверяем дискриминант////////////////////////////////////
    if (arg.x < 0)
    {
        cout<<"D<0! Net kornei!\n";
        return 1;
    }
    ////////////////Если он положительный - вычисляем корень/////////////////////
    CreateThread(NULL, 0, kor, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res1, sizeof(res1), &buf, NULL);
//  cout<<"sqrt(D)="<<res1<<"\n";
    ////////////////Подсчитываем 2а////////////////////////////////////
    arg.x = a;
    arg.y = 2;
    CreateThread(NULL, 0, um, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res2, sizeof(res2), &buf, NULL);
//  cout<<"2a="<<res2<<"\n";
    ////////////////Считаем -b+sqrt(D)////////////////////////////////////
    arg.x = 0 - b;
    arg.y = res1;
    CreateThread(NULL, 0, plus, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res3, sizeof(res3), &buf, NULL);
//  cout<<"-b+sqrt(D)="<<res3<<"\n";
    ////////////////Считаем -b-sqrt(D)////////////////////////////////////
    CreateThread(NULL, 0, minus, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &res1, sizeof(res1), &buf, NULL);
//  cout<<"-b-sqrt(D)="<<res1<<"\n";
    ////////////////Считаем корни по ф-ле (-b +- sqrt(d))/2a///////////////
    arg.x = res1;
    arg.y = res2;
    CreateThread(NULL, 0, del, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &x1, sizeof(x1), &buf, NULL);
    cout<<"x1 = "<<x1<<"\n";
    arg.x = res3;
    arg.y = res2;
    CreateThread(NULL, 0, del, &arg, 0, NULL);
    WaitForSingleObject(hSemaphore, INFINITE);
    ReadFile(hReadPipe, &x2, sizeof(x2), &buf, NULL);
    cout<<"x2 = "<<x2<<"\n";
    CloseHandle (hReadPipe);
    CloseHandle (hWritePipe);
    CloseHandle (hSemaphore);
    return 0;
}