ros/ros.h No such file or directory

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I have been running ROS Melodic in my Ubuntu Bionic system. I already had a previous workspace called 'catkin_ws'. Recently, I tried to create another workspace which I named 'ros'. I then created a directory called 'first_package' inside the 'src' folder using the 'catkin_create_pkg' command. I then coded a small segment which I have attached below and named it hello.cpp inside the 'first_package' which I have attached below.

//This is the ROS standard of "hello, world" program//

//This header defined standard ROS classed//
#include<ros/ros.h>

int main(int argc, char **argv){
//Initialize the ROS system
ros::init(argc, argv, "hello_ros");

//Establish this program as ROS node
ros::NodeHandle nh;

//Send some output as log message
ROS_INFO_STREAM("Hello, ROS!");
}

I have changed both the CMakeLists.txt and Package.xml accordingly, but I still receive this error. Could someone please resolve this issue. The error occurs when I use the command 'catkin_make'

This is the CMakeLists.txt file

cmake_minimum_required(VERSION 2.8.3)
project(first_package)
find_package(catkin REQUIRED COMPONENTS roscpp)
catkin_package()
include_directories()
add_executable(hello hello.cpp)
target_link_libraries(hello ${catkin_LIBRARIES})

The package.xml file is as follows,

<?xml version="1.0"?>
<package format="2">
  <name>first_package</name>
  <version>0.0.0</version>
  <description>The first_package package</description>
<maintainer email="danish@todo.todo">danish</maintainer>


 <license>TODO</license>
      <buildtool_depend>catkin</buildtool_depend>
      <build_depend>roscpp</build_depend>
      <exec_depend>roscpp</exec_depend>

<export>
  </export>
</package>