По введенному значению аргумента вычислить значение функции, заданной в виде графика

#include <windows.h>
#include <math.h>
#include <stdio.h>
 
#pragma comment(lib, "user32.lib")
#pragma comment(lib, "kernel32.lib")
#pragma comment(lib, "gdi32.lib")
 
 
#define _E 2.71828182845
#define _PI 3.14159265359
#define EPS 0.01
 
LRESULT CALLBACK WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
HDC hdc;
int j,center_x,center_y,mastab_x,mastab_y;
float i,fx,fx3, A,B,C, x1,y1,x2,y2;
HPEN hpen1,hpen2;
 
center_x = 300;
center_y = 300;
 
mastab_x = 10;
mastab_y = 10;
 
switch (uMsg)
{
case  WM_DESTROY:
PostQuitMessage(NULL);
return 0;
case WM_PAINT:
hpen1 = CreatePen(PS_SOLID, 1, RGB(255, 255, 128));
hpen2 = CreatePen(PS_SOLID, 1, RGB(0, 0, 0));
SelectObject(hdc, hpen2);
hdc = GetDC(hwnd);
MoveToEx(hdc, center_x , center_y, NULL); LineTo(hdc, 0,center_y);
MoveToEx(hdc, center_x , center_y, NULL); LineTo(hdc, center_x, 2 * center_y);
MoveToEx(hdc, center_x , center_y, NULL); LineTo(hdc, center_x, 0);
MoveToEx(hdc, center_x , center_y, NULL); LineTo(hdc, 2 * center_x, center_y);
for(i = -10.0; i < -6.0; i+=EPS)
{
fx = 16.0 - 4.0 * (64.0 + 16.0*i + i*i);
fx3 = (4.0 - sqrt(fx) ) / 2.0 ;
SetPixel(hdc, center_x + mastab_x * i, center_y - mastab_y * fx3, RGB(0,0,255) );
}
for(i = -6.0; i < -4.0; i+=EPS)
SetPixel(hdc, center_x + mastab_x * i, center_y - mastab_y * 2.0, RGB(0,0,255) );
 
x1 = -4.0;
y1 = 2.0;
x2 = 2.0;
y2 = -1.0;
A = y2 - y1;
B = -(x2 - x1);
C = -x1*A  - y1*B;
 
for(i = -4.0; i < 2.0; i+=EPS)
{
fx = (-C - A*i )/B;
SetPixel(hdc, center_x + mastab_x * i, center_y - mastab_y * fx, RGB(0,0,255) );
}
 
x1 = 2.0;
y1 = -1.0;
x2 = 4.0;
y2 = 1.0;
A = y2 - y1;
B = -(x2 - x1);
C = -x1*A  - y1*B;
 
for(i = 2.0; i < 4.0; i+=EPS)
{
fx = (-C - A*i )/B;
SetPixel(hdc, center_x + mastab_x * i, center_y - mastab_y * fx, RGB(0,0,255) );
}
 
 
ReleaseDC(hwnd, hdc);
DeleteObject(hpen1);
DeleteObject(hpen2);
return 0;
default:
return DefWindowProc(hwnd, uMsg,wParam, lParam);
}
 
return DefWindowProc(hwnd, uMsg,wParam, lParam);
}
 
int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrevInst, LPSTR CmdLine, int CmdShow)
{
WNDCLASSEX wc;
MSG msg;
HWND hwnd;
wc.cbSize = sizeof(WNDCLASSEX);
wc.style = CS_HREDRAW|CS_VREDRAW;
wc.lpfnWndProc = (WNDPROC) WndProc;
wc.cbClsExtra = NULL;
wc.cbWndExtra = NULL;
wc.hInstance = hInst;
wc.hbrBackground = (HBRUSH) GetStockObject(WHITE_BRUSH);
wc.lpszMenuName = NULL;
wc.lpszClassName =  "SimpleWinClass";
wc.hIcon = LoadIcon(NULL, IDI_APPLICATION);
wc.hIconSm =LoadIcon(NULL, IDI_APPLICATION);
wc.hCursor = LoadCursor(NULL, IDC_ARROW);
RegisterClassEx(&wc);
hwnd = CreateWindowEx(NULL, "SimpleWinClass", "Window", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, 
 
CW_USEDEFAULT, CW_USEDEFAULT, CW_USEDEFAULT,  NULL, NULL, hInst, NULL);
ShowWindow(hwnd, SW_SHOWNORMAL);
UpdateWindow(hwnd);
while (GetMessage(&msg, NULL, 0, 0))
{
TranslateMessage(&msg);
DispatchMessage(&msg);
}
return msg.wParam;
}
 
int main(int argc, char* argv[])
{
 
float x, y,A,B,C,fx,x1,y1,x2,y2;
scanf("%f", &x);
printf("%f\n", x);
 
if ( x >= -10.0 && x < -6.0)
{
fx =  ( 4.0 - sqrt ( 16.0 - 4.0 * (64.0 + 16.0*x + x*x) ) ) / 2.0;
printf("fx %f\n", fx);
}
else if (x >=-6 && x<-4)
{
fx = 2.0;
printf("fx %f\n", fx);
}
else if (x >=-4 && x<2)
{
x1 = -4.0;
y1 = 2.0;
x2 = 2.0;
y2 = -1.0;
A = y2 - y1;
B = -(x2 - x1);
C = -x1*A  - y1*B;
fx = (-C - A*x )/B;
printf("fx %f\n", fx);
}
else if (x >=2 && x<4)
{
x1 = 2.0;
y1 = -1.0;
x2 = 4.0;
y2 = 1.0;
A = y2 - y1;
B = -(x2 - x1);
C = -x1*A  - y1*B;
fx = (-C - A*x )/B;
printf("fx %f\n", fx);
}
 
HINSTANCE hInstance = GetModuleHandle(0);
LPSTR CommandLine = GetCommandLine();
return WinMain(hInstance, NULL,CommandLine, SW_SHOWDEFAULT);
return 0;
}

int WINAPI WinMain(HINSTANCE hInst, HINSTANCE hPrevInst, LPSTR CmdLine, int CmdShow)