Why are my 3d shapes in OpenGL/GLFW C++ missing faces

Question

So when i make a 3d triangle it just misses faces as shown below (with quad) any shape i try misses faces and you can just see straight through, (mind this is my first time using both OpenGL and GLFW)

The shape code is from a tutorial as ive tryed many shape codes to see if that was the issue and it seems it is not.

#include <glfw3.h>
#include <stdio.h>
#include <iostream>

using namespace std;

/* Begin Void prototyping */
void error_callback(int error, const char* description);
static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods);

int main(void)
{
    GLFWwindow* window;

    /* Initializes error call-backs */
    glfwSetErrorCallback(error_callback);

    /* Initialize the library */
    if (!glfwInit())
        return -1;

    /* Create a windowed mode window and its OpenGL context */
    window = glfwCreateWindow(640, 480, "Hello World", NULL, NULL); // fullscreen glfwGetPrimaryMonitor() (first NULL)
    if (!window)
    {
        glfwTerminate();
        return -1;
    }

    /* Makes OpenGL context current */
    glfwMakeContextCurrent(window);

    /* Make the window's context current */
    glfwMakeContextCurrent(window);

    /* Receives input events */
    glfwSetKeyCallback(window, key_callback);

    /* Loop until the user closes the window */
    while (!glfwWindowShouldClose(window))
    {
        /* Render here */
        float ratio;
        int width, height;

        glfwGetFramebufferSize(window, &width, &height);
        ratio = width / (float) height;

        glViewport(0, 0, width, height);
        glClear(GL_COLOR_BUFFER_BIT);

        glMatrixMode(GL_PROJECTION);
        glLoadIdentity();
        glOrtho(-ratio, ratio, -1.f, 1.f, 1.f, -1.f);
        glMatrixMode(GL_MODELVIEW);

        glLoadIdentity();
        glRotatef((float) glfwGetTime() * 50.f, 0.f, 0.f, 1.f);


    glBegin(GL_TRIANGLES);                              // Start Drawing A Triangle
        glColor3f(1.0f,0.0f,0.0f);                      // Red
        glVertex3f( 0.0f, 1.0f, 0.0f);                  // Top Of Triangle (Front)
        glColor3f(0.0f,1.0f,0.0f);                      // Green
        glVertex3f(-1.0f,-1.0f, 1.0f);                  // Left Of Triangle (Front)
        glColor3f(0.0f,0.0f,1.0f);                      // Blue
        glVertex3f( 1.0f,-1.0f, 1.0f);                  // Right Of Triangle (Front)
        glColor3f(1.0f,0.0f,0.0f);                      // Red
        glVertex3f( 0.0f, 1.0f, 0.0f);                  // Top Of Triangle (Right)
        glColor3f(0.0f,0.0f,1.0f);                      // Blue
        glVertex3f( 1.0f,-1.0f, 1.0f);                  // Left Of Triangle (Right)
        glColor3f(0.0f,1.0f,0.0f);                      // Green
        glVertex3f( 1.0f,-1.0f, -1.0f);                 // Right Of Triangle (Right)
        glColor3f(1.0f,0.0f,0.0f);                      // Red
        glVertex3f( 0.0f, 1.0f, 0.0f);                  // Top Of Triangle (Back)
        glColor3f(0.0f,1.0f,0.0f);                      // Green
        glVertex3f( 1.0f,-1.0f, -1.0f);                 // Left Of Triangle (Back)
        glColor3f(0.0f,0.0f,1.0f);                      // Blue
        glVertex3f(-1.0f,-1.0f, -1.0f);                 // Right Of Triangle (Back)
        glColor3f(1.0f,0.0f,0.0f);                      // Red
        glVertex3f( 0.0f, 1.0f, 0.0f);                  // Top Of Triangle (Left)
        glColor3f(0.0f,0.0f,1.0f);                      // Blue
        glVertex3f(-1.0f,-1.0f,-1.0f);                  // Left Of Triangle (Left)
        glColor3f(0.0f,1.0f,0.0f);                      // Green
        glVertex3f(-1.0f,-1.0f, 1.0f);                  // Right Of Triangle (Left)
    glEnd();                                            // Done Drawing The Pyramid


        /* Swap front and back buffers */
        glfwSwapBuffers(window);

        /* Poll for and process events */
        glfwPollEvents();
    }

    glfwDestroyWindow(window);

    glfwTerminate();
    return 0;
}

/* 
    Calls back the program if a GLFW function fail and logs it
*/
void error_callback(int error, const char* description)
{
    fputs(description, stderr);
}

/* Gives keys events */
static void key_callback(GLFWwindow* window, int key, int scancode, int action, int mods)
{
    switch(key)
    {
    case GLFW_KEY_ESCAPE:
        glfwSetWindowShouldClose(window, GL_TRUE);
        break;
    case GLFW_KEY_W:
        cout << "W works!!!" << endl;
        break;
    case GLFW_KEY_A:
        cout << "A works!!!" << endl;
        break;
    case GLFW_KEY_S:
        cout << "S works!!!" << endl;
        break;
    case GLFW_KEY_D:
        cout << "D works!!!" << endl;
        break;
    }
}

Ive been trying to fix it for hours i just dont know what too do now

Im using OpenGL 3+ with GLFW and C++

Answer 1

You need to enable depth testing:

glEnable(GL_DEPTH_TEST);
glDepthFunc(GL_LEQUAL);

Also, be sure to clear the depth buffer in addition to the color buffer:

glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);