add forward declaration examples

add classes

CPlusPlus/Classes/Vector3.h

@@ -0,0 +1,11 @@
+#pragma once
+
+struct Vector3
+{
+	float x;
+	float y;
+	float z;
+
+	Vector3() : x(0.0f), y(0.0f), z(0.0f) {}
+	Vector3(float _x, float _y, float _z) : x(_x), y(_y), z(_z) {}
+};