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Let's give a go at a very simple program that prints out "Hello World" to standard out (usually your monitor). We'll call our little program hello.c.
#include <stdio.h>
main() {
printf("Hello, world!\n");
return 0;
}
What's all this junk just to print out Hello, world!? Let's see what's happening:
Seems like trying to figure all this out is just way too confusing. Let's break things up one at at time:
return 0 statement. Seems like we are trying to
give something back, and it is an integer. Maybe if we modified
our main function definition:
int main() Ok, now we are saying that our
main function will be returning an integer! So remember,
you should always explicitly declare the return type on the
function!#include <stdlib.h> to our includes.
Let's change our return statement to
return EXIT_SUCCESS;. That is much more readable.
int printf(const char *format, ...); printf returns
an int. The man pages say that printf returns the number of
characters printed. Now you wonder, who cares? Why should you care
about this? It is good programming practice to ALWAYS check for
return values for important function calls. It will not only make your
program more readable,
but in the end it will make your programs less error prone./* */.
The comment begins with /* and ends with
*/.Let's see our new improved code!
#include <stdio.h>
#include <stdlib.h>
/* Main Function
* Purpose: Controls program, prints Hello, World!
* Input: Command-Line arguments
* Output: Returns Exit Status
*/
int main(int argc, char **argv) {
printf("Hello, world!\n");
return EXIT_SUCCESS;
}
The key point of this whole introduction is to
show you the fundamental difference between correctness and
understandability. Both sample codes produce the exact same
output in "Hello, world!" However, only the latter example shows
better readability in the code leading to code that is understandable.
All codes will have bugs. If you sacrifice code readability with
reduced (or no) comments and cryptic lines, the burden is shifted and
magnified when your code needs to be maintained.
Document what you can. Complex data types, function calls that may not
be obvious, etc. Good documentation goes a long way!
You will most likely be using the GNU C compiler, gcc in
a Linux or *nix-like environment. Some
environments will have the CC variable set which tends to
be suitable when using Makefiles.
A superficial look at compiling would entail: gcc file.c
But is this what you really want? We get a file called a.out in our
directory. This is because you aren't specifying the correct compiler
options. Taking the theory of "that which is learned first is learned
best", compile your programs using strict and pedantic
flags. This will not only catch more errors at compile time, but will
potentially help you create a program with less errors at run
time. The recommended options to include while compiling are:
So here is an example command line:
gcc -ansi -pedantic -Wall -O2 -o hello hello.c
This produces an executable called hello in the directory where
hello.c resides.
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