Your first
program is going to do is print the message "Hello World" on the screen. The program is a short one, to say the
least. Here it is:
#include
<stdio.h>
main()
{
printf("Hello
World\n");
}
The first line
is the standard start for all C programs - main().
After this comes the program's only instruction enclosed in curly brackets {}. The curly brackets mark the start
and end of the list of instructions that make up the program - in this case
just one instruction.
Notice the
semicolon marking the end of the instruction. You might as well get into the
habit of ending every C instruction with a semicolon - it will save you a lot
of trouble! Also notice that the semicolon marks the end of an instruction - it
isn't a separator as is the custom in other languages.
If you're
puzzled about why the curly brackets are on separate lines I'd better tell you
that it's just a layout convention to help you spot matching brackets. C is
very simple about the way you lay it out. For example, you could enter the program
as:
main(){printf("Hello World\n");} (but this is
unusual)
The printf function does what its name suggests it does: it prints, on the screen, whatever you tell it to. The "\n" is a special symbol that forces a new line on the screen.
That's enough explanation of our first program! Type it in and save it as Hello.c. Then use the compiler to compile it, then the linker to link it and finally run it. The output is as follows:
The printf function does what its name suggests it does: it prints, on the screen, whatever you tell it to. The "\n" is a special symbol that forces a new line on the screen.
That's enough explanation of our first program! Type it in and save it as Hello.c. Then use the compiler to compile it, then the linker to link it and finally run it. The output is as follows:
Hello World
A comment is a note to yourself (or
others) that you put into your source code. All comments are ignored by the
compiler. They exist solely for your benefit. Comments are used primarily to
document the meaning and purpose of your source code, so that you can remember
later how it functions and how to use it. You can also use the comment to
temporarily remove some lines of code. Simply surround the line(s) with the comment
symbols.
In C, the
start of a comment is signaled by the /*
character pair. A comment is ended by */.
For example, this is a syntactically correct C comment:
/* This is a
comment. */
Comments can
extend over several lines and can go anywhere except in the middle of any C
keyword, function name or variable name. In C you cannot have one comment within
another comment. That is comments may not be nested. Let's now look at our first
program one last time, but this time with comments:
#include
<stdio.h>
main()/* main function
heading */
{
printf("Hello
World\n"); /* display message on */
}
This program
is not large enough to write comment statements, but the principle is still
the same.