Hello World
<![CDATA[
/*
* File: hello.c
* -------------
* This program prints the message "Hello, world."
* on the screen. The program is taken from the
* classic C reference text "The C Programming
* Language" by Brian Kernighan & Dennis Ritchie.
*/
#include <stdio.h>
main()
{
printf("Hello, world.\n");
}
]]>
Compiling and running the program
<![CDATA[
lassie% ls
hello.c hello2.c
lassie% cc hello.c
lassie% ls
a.out hello.c hello2.c
lassie% a.out
Hello, world.
]]>
Note
- We compiled the program with cc
- the compiler created the file a.out , an executable file.
- type a.out to run your program
Annotated hello.c
<![CDATA[
/*
* File: hello.c
* -------------
* This program prints the message "Hello, world."
* on the screen. The program is taken from the
* classic C reference text "The C Programming
* Language" by Brian Kernighan & Dennis Ritchie.
*/
#include <stdio.h>
main()
{
printf("Hello, world.\n");
}
]]>
Notes
- the ".c" denotes a c source code file
- Comments lie between /* and */
- Library inclusions
- The #include preprocessor directives cause the header files
of libraries to be taken in by the C compiler.
- #include < xyzzy.h > -- for a standard system library
- The printf function
- Main program
Special Characters
The Program
<![CDATA[
/*
Program: hello2.c
Embellishments to hello.c.
*/
#include <stdio.h>
main()
{
printf("Mork says (in a loud voice): ") ;
printf("Hello world.\n\n") ;
printf("World says (whispers back): ") ;
printf("@$#%%\"\\!=@&*\n") ;
}
]]>
The Output
<![CDATA[
lassie% cc hello2.c
lassie% a.out
Mork says (in a loud voice): Hello world.
World says (whispers back): @$#%"\!=@&*
lassie%
]]>
Annotated hello2.c
<![CDATA[
/*
Program: hello2.c
Embellishments to hello.c.
*/
#include <stdio.h>
main()
{
printf("Mork says (in a loud voice): ") ;
printf("Hello world.\n\n") ;
printf("World says (whispers back): ") ;
printf("@$#%%\"\\!=@&*\n") ;
}
]]>
NOTE
- \n for newline
- %% for %
- \" for "
- \\ for \
Tradition
When Kernighan and Richie wrote the first book about the language C,
they used a simple program that printed out the string "Hello, World"
as the first example program.
Over the years, the traditional starting place for programming
discussions has become the "Hello, World" program.
Once you can print out a string, you've mastered the mechanics of
getting something to run without delving into the intricacies of
getting a real program to work the way you expect it to work.