Why is the triangle not drawn?

Question

OpenGL

Hello!
I'm trying to draw a triangle in CORE_PROFILE mode, it doesn't work:

int main() {
    glfwInit();
    glfwWindowHint(GLFW_CONTEXT_VERSION_MAJOR, 3);
    glfwWindowHint(GLFW_CONTEXT_VERSION_MINOR, 3);
    glfwWindowHint(GLFW_OPENGL_PROFILE, GLFW_OPENGL_CORE_PROFILE);
    glfwWindowHint(GLFW_RESIZABLE, GL_FALSE);
    GLFWwindow* window = glfwCreateWindow(800, 600, "first", 0, 0);
    if (window == 0)
    {
        //std::cout << "Failed to create GLFW window" << std::endl;
        glfwTerminate();
        return -1;
    }
    glfwMakeContextCurrent(window);
    glewExperimental = GL_TRUE;
    if (glewInit() != GLEW_OK)
    {
        std::cout << "Failed to initialize GLEW" << std::endl;
        return -1;
    }
    int width, height;
    glfwGetFramebufferSize(window, &width, &height);
    glViewport(0, 0, width, height);
    const GLchar* const vertexSource =
            "#version 330 core\n"
            "layout (location=0) in vec3 position;"
            "void main(){"
            "gl_Position = vec4(position.x, position.y, position.z, 1.0f);}\0";

    const GLchar* const fragmentSource =
            "#version 330 core\n"
            "out vec4 color;"
            "void main(){"
            "color = vec4(1.0f, 0.5f, 0.2f, 1.0f);}\0";

    GLuint vertexShader;
    vertexShader = glCreateShader(GL_VERTEX_SHADER);
    glShaderSource(vertexShader, 1, &vertexSource, NULL);
    glCompileShader(vertexShader);
    GLint success;
    GLchar infoLog[512];
    glGetShaderiv(vertexShader, GL_COMPILE_STATUS, &success);
    if(!success)
    {
        glGetShaderInfoLog(vertexShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::VERTEX::COMPILATION_FAILED\n" << infoLog << std::endl;

    }else{
        cout << "Success init vertex shader\n";
    }
    GLuint fragmentShader;
    vertexShader = glCreateShader(GL_FRAGMENT_SHADER);
    glShaderSource(fragmentShader, 1, &fragmentSource, NULL);
    glCompileShader(fragmentShader);
    glGetShaderiv(fragmentShader, GL_COMPILE_STATUS, &success);
    if(!success)
    {
        glGetShaderInfoLog(fragmentShader, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;

    }else{
        cout << "Success init fragment shader\n";
    }



    GLuint shaderProgram;
    shaderProgram = glCreateProgram();

    glAttachShader(shaderProgram, vertexShader);
    glAttachShader(shaderProgram, fragmentShader);
    glLinkProgram(shaderProgram);
    glGetProgramiv(shaderProgram, GL_LINK_STATUS, &success);
    if(!success)
    {
        glGetProgramInfoLog(shaderProgram, 512, NULL, infoLog);
        std::cout << "ERROR::SHADER::FRAGMENT::COMPILATION_FAILED\n" << infoLog << std::endl;

    }else{
        cout << "Success link shader's program\n";
    }

    glDeleteShader(vertexShader);
    glDeleteShader(fragmentShader);


    GLuint VBO, VAO;
    glGenBuffers(1, &VBO);
    glGenVertexArrays(1, &VAO);
    glBindVertexArray(VAO);

    GLfloat vertexTriangle[] = {
      -0.5f, -0.5f, 0.0f,
       0.5f, -0.5f, 0.0f,
       0.0f,  0.5f, 0.0f
    };

    glBindBuffer(GL_ARRAY_BUFFER, VBO);
    glBufferData(GL_ARRAY_BUFFER, sizeof(vertexTriangle), vertexTriangle, GL_DYNAMIC_DRAW);

    glVertexAttribPointer(0, 3, GL_FLOAT, GL_FALSE, 3 * sizeof(GLfloat), (GLvoid*)0);
    glEnableVertexAttribArray(0);

    glBindBuffer(GL_ARRAY_BUFFER, 0);
    glBindVertexArray(0);


    while(!glfwWindowShouldClose(window))
    {
        glClearColor(0.2f, 0.3f, 0.3f, 1.0f);
        glClear(GL_COLOR_BUFFER_BIT);

        // draw our first triangle
        glUseProgram(shaderProgram);
        glBindVertexArray(VAO); // seeing as we only have a single VAO there's no need to bind it every time, but we'll do so to keep things a bit more organized
        glDrawArrays(GL_TRIANGLES, 0, 3);
        glBindVertexArray(0); // no need to unbind it every time

        // glfw: swap buffers and poll IO events (keys pressed/released, mouse moved etc.)
        // -------------------------------------------------------------------------------
        glfwSwapBuffers(window);
        glfwPollEvents();
    }

    glfwTerminate();
    return 0;
}

I pass all the vertices to the VBO, the shaders compile successfully, and only a gray screen appears on the screen. Please tell me why this might be