Compiling a source file
A special feature of Dev-C++ is the ability to compile (and run) single source files. This is done via the following steps:

- Create (Ctrl+N) or open (Ctrl+O) a source file.
- Click Compile (F9) to compile the currently visible file.
- Optionally, run the created executable (F10).

This compilation will use the compiler set selected at Tools >> Compiler Options.
Compiling a project
Compiling a project largely requires the same steps:

- Create (Ctrl+N) or open (Ctrl+O) a project.
- Click Compile (F9) to apply changes made in a source file.
- Click Rebuild (F12) to apply changes made in a header file or to recompile all files.
- Optionally, run the created executable (F10).

This compilation will use the compiler set selected at Tools >> Compiler Options, but unlike source file compilations, it will use the compiler settings located at Project >> Project Options >> Compiler.
Tips

- For single file compilations, make sure to use proper file extensions. When not explicitly telling the compiler which standard to use (using the -std flag), use *.c to compile as C or *.cpp to compile as C++.
- To reduce compilation output size, especially when using C++ headers, consider passing -s to the compiler. This can be done manually or via (Settings) >> Linker >> Strip executable. This option will remove any unused data from the output. A downside of this option is that debugging and profiling will not work anymore. An alternative but much less effective approach is to reduce the amount of included files.
- To reduce compilation time, consider including less files. For example, when using a project, don't blindly include every file in every file!
- To save one click in the compilation process, try out Compile & Run (F11). This will, obviously, compile and run your file or project immediately afterwards.
- When changing a header file, make sure to recompile all source files that make use of it by rebuilding. Not doing so will lead to undefined executable behaviour: the code you're seeing will not be what will be executed because some source files are making use of outdated headers.