Программа выдаёт ошибку: warning C4244

#include "stdafx.h"
#include <iostream>
#include <conio.h>
#include <cmath>
 
using namespace std;
double const a,b = 1;
double const PI = 3.14159265358979323846;
 
void F1(double x)
{
    float f;
    
    f = a * x + tan(x) * sqrt(log(abs(x +-5)));
 
    cout << "F = " << f << endl;
}
 
void F2(double x)
{
    float f;
 
    f = (x * x - b * b ) * cos(PI);
 
    cout << "F = " << f << endl;
}
 
void F3(double x)
{
    float f;
 
    f = (x - 2) * sin((2 * PI) * x);
 
    cout << "F = " << f << endl;
}
 
void main()
{
    double x0, xk, h;
 
    cout << "Enter the x0 = ";
    cin >> x0;
    cout << "Enter the xk = ";
    cin >> xk;
    cout << "Enter the h = ";
    cin >> h;
 
    while(x0 <= xk)
    {
        if (x0 < -2) F1(x0);
        if (x0 == -2) F2(x0);
        if (x0 > -2) F3(x0);
 
        x0 += + h;
    }
 
    _getch();
}

double const a,b = 1;
double const PI = 3.14159265358979323846;

double a,b = 1;
double PI = 3.14159265358979323846;