Compiler gives SyntaxErrors, which are not shown in VisualStudio. What can I do?

I'm about to teach myself OpenGL in C++ and VisualStudio says my Code is OK. But if I compile the Code I get many Syntax errors. I really dont understand it.

Here is the Error Message:

1>------ Erstellen gestartet: Projekt: OpenGL, Konfiguration: Release Win32 ------
1>Application.cpp
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Engine.h(50,25): error C2061: Syntaxfehler: Bezeichner "Renderer"
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Application.cpp(35,33): error C2660: "Engine::gameLoop": Funktion akzeptiert keine 3 Argumente
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Engine.h(50,7): message : Siehe Deklaration von "Engine::gameLoop"
1>Buffers.cpp
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(13,26): error C3646: "parseShader": Unbekannter Überschreibungsspezifizierer
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(13,26): error C2059: Syntaxfehler: "("
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(13,54): error C2238: Unerwartete(s) Token vor ";"
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(22,39): error C2061: Syntaxfehler: Bezeichner "GameVars"
1>Engine.cpp
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(13,26): error C3646: "parseShader": Unbekannter Überschreibungsspezifizierer
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(13,26): error C2059: Syntaxfehler: "("
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(13,54): error C2238: Unerwartete(s) Token vor ";"
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(22,39): error C2061: Syntaxfehler: Bezeichner "GameVars"
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Engine.cpp(72,12): error C2660: "Renderer::render": Funktion akzeptiert keine 2 Argumente
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Renderer.h(22,7): message : Siehe Deklaration von "Renderer::render"
1>Renderer.cpp
1>C:\Users\schko\source\repos\OpenGL\OpenGL\src\Engine.h(50,25): error C2061: Syntaxfehler: Bezeichner "Renderer"
1>Die Erstellung des Projekts "OpenGL.vcxproj" ist abgeschlossen -- FEHLER.
========== Erstellen: 0 erfolgreich, 1 fehlerhaft, 0 aktuell, 0 übersprungen ==========

And this is my Code...

Application.cpp:

#include "Buffers.h"
#include "Renderer.h"
#include "Engine.h"

int main()
{
    float vertices[] =
    {
            -0.5f, -0.5f, // 0
             0.5f, -0.5f, // 1
             0.5f,  0.5f, // 2
            -0.5f,  0.5f  // 3
    };

    unsigned int indices[] =
    {
        0, 1, 2,
        2, 3, 0
    };

    Buffers buff(vertices, indices, 4 * 2, 6);
    Renderer r;
    Engine engine;

    if (engine.err != 0)
        return -1;

    float g = 0.0f;
    float b = 1.0f;
    float iG = 0.05f;
    float iB = -0.05f;

    GameVars vars = { 0.0f, g, b, 1.0f };

    engine.gameLoop(r, buff, engine);

    while (!engine.terminated)
    {
        if (g > 1.0f)
            iG = -0.005f;
        else if (g < 0.0f)
            iG = 0.005f;

        if (b > 1.0f)
            iB = -0.005f;
        else if (b < 0.0f)
            iB = 0.005f;

        g += iG;
        b += iB;

        engine.setVars({ 0.0f, g, b, 1.0f });
    }

    buff.~Buffers();
    r.~Renderer();
    engine.~Engine();

    return 0;
}

Engine.cpp:

#include "Engine.h"

void GLClearError()
{
    while (glGetError() != GL_NO_ERROR);
}

bool GLLogCall(const char* function, const char* file, int line)
{
    while (GLenum error = glGetError())
    {
        std::cout << "[OpenGL Error] (" << error << ") at " << function << " in " << file << " on line " << line << std::endl;
        return false;
    }

    return true;
}

Engine::Engine()
{
    err = init();
    terminated = false;
    std::cout << glGetString(GL_VERSION) << std::endl;
}

Engine::~Engine()
{
    glfwTerminate();
}

int Engine::init()
{
    if (!glfwInit())
    {
        std::cout << "Init of GLFW failed!" << std::endl;
        return -1;
    }

    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);

    window = glfwCreateWindow(1020, 760, "MyLearningApplication", NULL, NULL);
    if (!window)
    {
        std::cout << "Creating the Window failed!" << std::endl;
        glfwTerminate();
        return -1;
    }

    glfwMakeContextCurrent(window);

    glfwSwapInterval(1);

    if (glewInit() != GLEW_OK)
    {
        std::cout << "Init of GLEW failed!" << std::endl;
        return -1;
    }

    return 0;
}

void Engine::gameLoop(Renderer renderer, Buffers buffer, Engine This)
{
    std::thread thread([](Renderer renderer, Buffers buffer, Engine eng) {

        while (!glfwWindowShouldClose(eng.getWindow()))
        {
            GLCall(glClear(GL_COLOR_BUFFER_BIT));

            renderer.render(buffer, eng.getVars());

            glfwSwapBuffers(eng.getWindow());
            glfwPollEvents();
        }

        eng.terminated = true;

    }, renderer, buffer, This);
}

Engine.h:

#pragma once

#include <GL/glew.h>
#include <GLFW/glfw3.h>

#include "Buffers.h"
#include "Renderer.h"

#include <iostream>
#include <string>
#include <thread>

#define ASSERT(x) if (!(x)) __debugbreak();
#define GLCall(x)\
        GLClearError();\
        x;\
        ASSERT(GLLogCall(#x, __FILE__, __LINE__));

void GLClearError();
bool GLLogCall(const char* function, const char* file, int line);

struct ShaderSource
{
    std::string VertexSource;
    std::string FragmentSource;
};

struct GameVars
{
    float r;
    float g;
    float b;
    float alpha;
};

class Engine
{
private:
    GLFWwindow* window;
    GameVars vars;
    int init();

public:
    int err;
    bool terminated;

    Engine();
    ~Engine();

    void gameLoop(Renderer renderer, Buffers buffer, Engine This);
    inline GLFWwindow* getWindow() const { return window; }
    inline GameVars getVars() const { return vars; }
    inline void setVars(GameVars newVars) { vars = newVars; }
};

Renderer.cpp:

#include "Renderer.h"

#include <iostream>
#include <fstream>
#include <string>
#include <sstream>

Renderer::Renderer()
{
    ShaderSource source = parseShader("res/shaders/basic.shader");
    m_Shader1 = createShader(source.VertexSource, source.FragmentSource);

    GLCall(glUseProgram(m_Shader1));
    GLCall(m_uVar1 = glGetUniformLocation(m_Shader1, "u_Color"));

    GLCall(glUseProgram(0));
}

Renderer::~Renderer()
{
    GLCall(glDeleteProgram(m_Shader1));
}

ShaderSource Renderer::parseShader(const std::string filePath)
{
    std::ifstream stream(filePath);

    enum class ShaderType
    {
        NONE = -1, VERTEX = 0, FRAGMENT = 1
    };

    std::string line;
    std::stringstream ss[2];
    ShaderType type = ShaderType::NONE;
    while (getline(stream, line))
    {
        if (line.find("#shader") != std::string::npos)
        {
            if (line.find("vertex") != std::string::npos)
                type = ShaderType::VERTEX;
            else if (line.find("fragment") != std::string::npos)
                type = ShaderType::FRAGMENT;
        }
        else
        {
            ss[(int)type] << line << "\n";
        }
    }

    return { ss[0].str(), ss[1].str() };
}

unsigned int Renderer::compileShader(unsigned int type, std::string source)
{
    GLCall(unsigned int id = glCreateShader(type));
    const char* src = source.c_str();
    GLCall(glShaderSource(id, 1, &src, nullptr));
    GLCall(glCompileShader(id));

    int result;
    GLCall(glGetShaderiv(id, GL_COMPILE_STATUS, &result));
    if (result == GL_FALSE)
    {
        int length;
        GLCall(glGetShaderiv(id, GL_INFO_LOG_LENGTH, &length));
        char* msg = (char*)alloca(length * sizeof(char));
        GLCall(glGetShaderInfoLog(id, length, &length, msg));
        std::cout << "Failed to compile " << (type == GL_VERTEX_SHADER ? "vertex" : "fragment") << "shader!" << std::endl;
        std::cout << msg << std::endl;
        return 0;
    }

    return id;
}

unsigned int Renderer::createShader(std::string vertexShader, std::string fragmentShader)
{
    GLCall(unsigned int program = glCreateProgram());
    unsigned int vs = compileShader(GL_VERTEX_SHADER, vertexShader);
    unsigned int fs = compileShader(GL_FRAGMENT_SHADER, fragmentShader);

    GLCall(glAttachShader(program, vs));
    GLCall(glAttachShader(program, fs));
    GLCall(glLinkProgram(program));
    GLCall(glValidateProgram(program));

    GLCall(glDeleteShader(vs));
    GLCall(glDeleteShader(fs));

    return program;
}

Buffers Renderer::createBuffer(const void* vertices, const unsigned int* indices, unsigned int vertexCount, unsigned int indexCount)
{
    Buffers newB(vertices, indices, vertexCount, indexCount);
    return newB;
}

void Renderer::render(Buffers buffer, GameVars vars)
{
    buffer.bind();

    GLCall(glUseProgram(m_Shader1));

    GLCall(glUniform4f(m_uVar1, vars.r, vars.g, vars.b, vars.alpha));
    GLCall(glDrawElements(GL_TRIANGLES, 6, GL_UNSIGNED_INT, nullptr));

    GLCall(glUseProgram(0));

    buffer.unbind();
}

Renderer.h:

#pragma once

#include "Engine.h"
#include "Buffers.h"

class Renderer
{
private:
    unsigned int m_Shader1;
    unsigned int m_uVar1;
    ShaderSource parseShader(const std::string filePath);
    unsigned int compileShader(unsigned int type, std::string source);
    unsigned int createShader(std::string vertexShader, std::string fragmentShader);

public:
    Renderer();
    ~Renderer();

    Buffers createBuffer(const void* vertices, const unsigned int* indices, unsigned int vertexCount, unsigned int indexCount);
    void render(Buffers buffer, GameVars vars);
};

Buffers.cpp:

#include "Buffers.h"

#include "Engine.h"

Buffers::Buffers(const void* vertices, const unsigned int* indices, unsigned int vertexCount, unsigned int indexCount)
    : m_iCount(indexCount)
{
    ASSERT(sizeof(unsigned int) == sizeof(GLuint));

    GLCall(glGenVertexArrays(1, &m_vaoID));
    GLCall(glBindVertexArray(m_vaoID));

    GLCall(glGenBuffers(1, &m_vBuffID));
    GLCall(glBindBuffer(GL_ARRAY_BUFFER, m_vBuffID));
    GLCall(glBufferData(GL_ARRAY_BUFFER, vertexCount * sizeof(float), vertices, GL_STATIC_DRAW));

    GLCall(glEnableVertexAttribArray(0));
    GLCall(glVertexAttribPointer(0, 2, GL_FLOAT, GL_FALSE, 2 * sizeof(float), 0));

    GLCall(glGenBuffers(1, &m_iBuffID));
    GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_iBuffID));
    GLCall(glBufferData(GL_ELEMENT_ARRAY_BUFFER, indexCount * sizeof(GLuint), indices, GL_STATIC_DRAW));

    GLCall(glBindBuffer(GL_ARRAY_BUFFER, 0));
}

Buffers::~Buffers()
{
    GLCall(glDeleteBuffers(1, &m_iBuffID));
    GLCall(glDeleteBuffers(1, &m_vBuffID));
    GLCall(glDeleteVertexArrays(1, &m_vaoID));
}

void Buffers::bind() const
{
    GLCall(glBindVertexArray(m_vaoID));
    GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, m_iBuffID));
}

void Buffers::unbind() const
{
    GLCall(glBindVertexArray(0));
    GLCall(glBindBuffer(GL_ELEMENT_ARRAY_BUFFER, 0));
}

Buffers.h:

#pragma once

class Buffers
{
private:
    unsigned int m_iBuffID;
    unsigned int m_vBuffID;
    unsigned int m_vaoID;
    unsigned int m_iCount;

public:
    Buffers(const void* vertices, const unsigned int* indices, unsigned int vertexCount, unsigned int indexCount);
    ~Buffers();

    void bind() const;
    void unbind() const;

    inline unsigned int getIndexCount() { return m_iCount; }
};

Shader was working fine.