Creating the program
• A programmer uses a text editor to create or modify files containing C code
• The contents must obey C syntax
• The filename must end by convention “.c”
Ex: sample.c
• Code is also known as source code
• A file containing source code is called a source file
Compiling the program
• There are many C compilers around.
• Sun compiler - cc
• GNU C - gcc
• Borland compiler, Turbo C compiler, Quick C compiler
• root@home> gcc –Wall sample.c
• Note: There may be a minor variations of
library functions between different compilers
Running the sample program in Linux based Operating Systems
• If there are no errors in sample.c, this command produces an executable file in the same directory by name a.out
• root@home> ./a.out
• This executes your program, printing any results to the screen
Structure of C program
program header comment
preprocessor directives (if any)
int main ( )
{
statement(s)
return 0 ;
}
Description of hello.c
Comments
Preprocessor Directives
int main ()
The Function Body
printf (“Hello, World!\n”) ;
return 0
• A programmer uses a text editor to create or modify files containing C code
• The contents must obey C syntax
• The filename must end by convention “.c”
Ex: sample.c
• Code is also known as source code
• A file containing source code is called a source file
Compiling the program
• There are many C compilers around.
• Sun compiler - cc
• GNU C - gcc
• Borland compiler, Turbo C compiler, Quick C compiler
• root@home> gcc –Wall sample.c
• Note: There may be a minor variations of
library functions between different compilers
Running the sample program in Linux based Operating Systems
• If there are no errors in sample.c, this command produces an executable file in the same directory by name a.out
• root@home> ./a.out
• This executes your program, printing any results to the screen
Structure of C program
program header comment
preprocessor directives (if any)
int main ( )
{
statement(s)
return 0 ;
}
Description of hello.c
- A C program starts execution with a function called main()
- When a C program is started by the OS, a special startup routine is called before main().
- This startup routine takes values from the OS (command line arguments and the environment) and sets things up so that main() is called first.
- The startup routine also invoked exit() on return from main(). exit() releases all to reusable resources and then return to the kernel
Comments
- A comment is descriptive text used to help a reader of the program understand its content.
- All comments must begin with characters /*and end with the characters */.
- These are called comment delimiters.
- Nested comments are not allowed.
Preprocessor Directives
- Lines that begin with a # are called preprocessor directives
- Example: the #include <stdio.h> directive causes the preprocessor to include a copy of the standard input/output header file stdio.h at this point in the code.
- This header file was included because it contains information about the printf ( ) function that is used in this program.
int main ()
- Every program must have a function called main. This is where program execution begins.
- The reserved word “int” indicates that main() returns an integer value.
- The parentheses following the reserved word “main” indicate that it is a function
The Function Body
- A left brace (curly bracket) -- { -- begins the body of every function.
- A corresponding right brace -- } -- ends the function body
printf (“Hello, World!\n”) ;
- This line is a C statement
- It is a call to the function printf ( ) with a single argument (parameter), namely the string “Hello, World!\n”
- Notice that this line ends with a semicolon
- Note: All statements in C end with a semicolon
return 0
- Because function main() returns an integer value, there must be a statement that indicates what this value is.
- The statement “return 0 ;” indicates that main() returns a value of zero to the operating system.
- A value of 0 indicates that the program successfully terminated execution.
- Don't worry about this concept now. Just remember to use the statement.
