In this example, the iostream standard library file is included by an include directive. The preprocessor inserts into the source code all files included by the include directives. The preprocessor is a program that scans the source code for preprocessor directives such as include directives. These programs are, in their order of appearance: Three programs are used to translate your source code into an executable file that the computer can run. Computers don’t understand C++ or any other programming language. While you now understand “My First C++ Program” code, the computer won’t. This is often referred to as mixed-language programming.
Program routines can be created in other languages and compiled into object modules and then later linked with object modules created with C++. The second item of interest is the assembly code file and assembler step shown at the bottom.
These are #include, #ifndef, #define, and #endif. These special preprocessor instructions are called preprocessor directives. The C++ preprocessor acts upon special instructions that can be contained in the C++ source code. First, C++ adds a preprocessing step to the program creation process. Two interesting points to note in figure above.
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