What is the syntax of writing a header file?

A header file in C or C++ typically has a .h extension and contains declarations for functions, macros, constants, and data types. The syntax includes include guards to prevent multiple inclusions, which are implemented using #ifndef, #define, and #endif preprocessor directives. For example:

<code class="language-c">#ifndef MY_HEADER_H
#define MY_HEADER_H
void myFunction();
#endif // MY_HEADER_H
</code>

This structure ensures that the contents of the header file are included only once in a compilation unit.