<pre><code class="lang-cpp">#include &lt;iostream&gt;
#include "distance.h"

int main() {

 std::cout &lt;&lt; distance(3, 4, 5) &lt;&lt; std::endl; 
 std::cout &lt;&lt; distance(7.0, 2.1, 5.4) &lt;&lt; std::endl;

 return 0; 
}
</code></pre>
<h1 id="heading-function-declaration">Function declaration</h1>
write the function declaration in "functionname.h" file.
Include "functionname.h":paste declaration in the main.cpp.
include" " : search the file from current dictionary.
include&lt;&gt; :search the file from where the library install.
<h1 id="heading-function-definition">Function definition</h1>
write the function definition in "functionname.cpp" file.
use 'g++ main.cpp functionname.cpp' to compile the whole code.

```cpp
#include <iostream>
#include "distance.h"

int main() {

 std::cout << distance(3, 4, 5) << std::endl; 
 std::cout << distance(7.0, 2.1, 5.4) << std::endl;
 
 return 0; 
}
```

# Function declaration

write the function declaration in "functionname.h" file.

Include "functionname.h":paste declaration in the main.cpp.

include" " : search the file from current dictionary.

include&lt;&gt; :search the file from where the library install.

# Function definition

write the function definition in "functionname.cpp" file.

use 'g++ main.cpp functionname.cpp' to compile the whole code.

C++(func seperate&file organize)

Function declaration

Function definition