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PREPROCESSOR COMMANDS IN C
The C compiler is made of two functional parts, a preprocessor and a translator. The preprocessor uses programmer-supplied commanmds to prepare the source
program for compilation. The translator converts the statements into machine code that it places in an object module.
The preprocessor can be thought of as a smart editor. like a smart editor it inserts, includes, and replaces text based on commands supplied by the programmer.
In this case, however the commands are made a permanent part of the source program.
All preprocessor commands start with a pound sign (#). Some of the traditional compilers require the pound sign to be in the first column. ABSi/ISO C specifies that
it can be anywhere on the line. preprocessor commands can be placed anywhere in the program. To distinguish a preprocessor command and a program
command, the preprocessor commands are often called commands.