# Writing a Hello World Program


The following exemplifies how to run the first program on the development board. The created program outputs the message "Hello World!" .


## Example Directory

The complete code directory is as follows:

  
```
applications/sample/hello
│── BUILD.gn
│── include
│   └── helloworld.h
│── src
│   └── helloworld.c
├── bundle.json
build
└── subsystem_config.json
vendor/hihope
└── rk3568
    └── config.json
```


## How to Develop

Perform the steps below in the source code directory:

1. Create a directory and write the service code.

   Create the **applications/sample/hello/src/helloworld.c** directory and file whose code is shown in the following example. You can customize the content to be printed. For example, you can change **World** to **OHOS**. Declare the string printing function **HelloPrint** in the **helloworld.h** file. You can use either C or C++ to develop a program.

     
   ```
   #include <stdio.h>
   #include "helloworld.h"
   
   int main(int argc, char **argv)
   {
       HelloPrint();
       return 0;
   }
   
   void HelloPrint()
   {
       printf("\n\n");
       printf("\n\t\tHello World!\n");
       printf("\n\n");
   }
   ```

   Add the header file **applications/sample/hello/include/helloworld.h**. The sample code is as follows:

     
   ```
   #ifndef HELLOWORLD_H
   #define HELLOWORLD_H
   #ifdef __cplusplus
   #if __cplusplus
   extern "C" {
   #endif
   #endif
   
   void HelloPrint();
   
   #ifdef __cplusplus
   #if __cplusplus
   }
   #endif
   #endif
   #endif // HELLOWORLD_H
   ```

2. Create a build file.

   1. Create the **applications/sample/hello/BUILD.gn** file. The file content is as follows:
         
       ```
       import("//build/ohos.gni") # Import the build template.
       ohos_executable("helloworld") {# Executable module.
         sources = [       # Source code of the module.
           "src/helloworld.c"
         ]
         include_dirs = [  # Directory of header file on which the module depends.
           "include" 
         ]
         cflags = []
         cflags_c = []
         cflags_cc = []
         ldflags = []
         configs = []
         deps =[]    # Internal dependencies of a component.
         part_name = "hello"    # Component name. This parameter is mandatory.
         install_enable = true # Whether to install the software by default. This parameter is optional. By default, the software is not installed.
       }
       ```
   2. Create the **applications/sample/hello/bundle.json** file and add the description of the **sample** component. The content is as follows:
         
       ```
       {
           "name": "@ohos/hello",
           "description": "Hello world example.",
           "version": "3.1",
           "license": "Apache License 2.0",
           "publishAs": "code-segment",
           "segment": {
               "destPath": "applications/sample/hello"
           },
           "dirs": {},
           "scripts": {},
           "component": {
               "name": "hello",
               "subsystem": "sample",
               "syscap": [],
               "features": [],
               "adapted_system_type": [ "mini", "small", "standard" ],
               "rom": "10KB",
               "ram": "10KB",
               "deps": {
                   "components": [],
                   "third_party": []
               },
               "build": {
                   "sub_component": [
                       "//applications/sample/hello:helloworld"
                   ],
                   "inner_kits": [],
                   "test": []
               }
           }
       }
       ```

       The **bundle.json** file consists of two parts. The first part describes the information about the subsystem to which the component belongs, and the second part defines the component building configuration. When adding a part, you need to specify the **sub_component** contained in the part. If there are interfaces provided for other components, describe them in **inner_kits**. If there are test cases, describe them in **test**.

3. Modify the subsystem configuration file.

   Add the configuration of the new subsystem to the **build/subsystem_config.json** file.

     
   ```
   "sample": {
       "path": "applications/sample/hello",
       "name": "sample"
     },
   ```

4. Modify the product configuration file.

     In the vendor\hihope\rk3568\config.json file, add the hello part after the existing part.
     
   ```
       "usb:usb_manager_native":{},
       "applications:prebuilt_hap":{},
       "sample:hello":{},
       "wpa_supplicant-2.9:wpa_supplicant-2.9":{},
   ```