The document explains the basic programming structure in C, focusing on preprocessors, header files, and the role of the linker. It details how preprocessor directives, denoted by the '#' symbol, manage code before compilation, and specifically references common header files like stdio.h and their functions. Additionally, it differentiates between 'int main()' and 'int main(void)', and outlines the linking process that combines various code modules into an executable file.

1. Understanding Basic
Programming Structure of C

8. C Preprocessors
• As the name suggests Preprocessors are programs that process our source
code before compilation.

9. • In C, all lines that begin with # are directives for the
preprocessor, which means that all these directives will be
processed before the program is actually compiled. The
#include directive includes the contents of a file during
compilation. In this case, the file stdio.h is added in the
source program before the actual compilation begins.
• stdio.h
is a header file that comes with the C compiler and contains
information about input and output functions, e.g., printf()

10. Header files
A header file is a file containing C declarations and macro
definitions to be shared among the source files, compiler,
preprocessor, C library, and other header files.
In C, the usual convention is to give header files names
that end with .h.
•
The ISO C standard library consists of 24 header
files which can be included into a programmer’s project with
a single directive. Each header file contains one or more
function declarations, data type definitions, and macros.

12. • In C, all lines that begin with # are directives for the
preprocessor, which means that all these directives will be
processed before the program is actually compiled. The
#include directive includes the contents of a file during
compilation. In this case, the file stdio.h is added in the
source program before the actual compilation begins.
• stdio.h
is a header file that comes with the C compiler and contains
information about input and output functions, e.g., printf()

13. Header files
A header file is a file containing C declarations and macro
definitions to be shared among the source files, compiler,
preprocessor, C library, and other header files.
In C, the usual convention is to give header files names
that end with .h.
•
The ISO C standard library consists of 24 header
files which can be included into a programmer’s project with
a single directive. Each header file contains one or more
function declarations, data type definitions, and macros.

14. Some of C Header files:
• stdio.h – Standard Input Output. Defines core input and output functions.
stdio.h is a header file which has the necessary information to include the
input/output related functions in our program. Example printf, scanf etc.
• conio.h –console input/output. Some of its most commonly used
functions are clrscr, getch, etc. They can be used to clear screen, change
color of text and background, eyc
• string.h – Defines string handling functions
• math.h – Defines common mathematical functions

15. Difference between “int main()” and “int main(void)”

16. • int main() can be called with any number of arguments
• int main(void) can only be called without any argument.
• Although it doesn’t make any difference most of the times, using “int
main(void)” is a recommended practice in C

17. • Preprocessor programs provide preprocessors directives which tell
the compiler to preprocess the source code before compiling.
• All of these preprocessor directives begin with a ‘#’ (hash) symbol.
The ‘#’ symbol indicates that, whatever statement starts with #, is
going to the preprocessor program, and preprocessor program will
execute this statement.

18. • The C Preprocessor is not a part of the compiler, but is a separate step in the compilation process.
• In simple terms, a C Preprocessor is just a text substitution tool and it instructs the compiler to do
required pre-processing before the actual compilation.
• #define
• Substitutes a preprocessor macro.
• #include
• Inserts a particular header from another file.

19. • #include <stdio.h>
• #include "myheader.h“
• #define MAX_ARRAY_LENGTH 20

20. • 1) When we use include directive, the contents of included header file
(after preprocessing) are copied to the current file.
• 2) When we use define for a constant, the preprocessor produces a C
program where the defined constant is searched and matching tokens are
replaced with the given expression. For example in the following program
max is defined as 100.

21. #include <stdio.h>
#define max 100
int main()
{
printf("max is %d", max);
return 0;
}

22. Linker
• A linker is a program in a system, also known as a link editor and
binder, which combines object modules into a single object file.
• Generally, it is a program that performs the process of linking; it takes
one or multiple object files, which are generated by compiler. And,
then combines these files into an executable files.
• Modules are called for the different pieces of code, which are written
in programming languages.
• Linking is a process that helps to gather and maintain a different piece
of code into an executable file or single file.

24. • The linker is a program in a system, also known as link editor and
binder, which combines object modules into a single object file.
• The loader is a special program that loads the executable module of a
program that is generated by the linker and prepares this code for
execution by a computer.

27. Adding 2 Numbers