Programming in C - Editing Your First Program
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You could try altering the same program to display something else on the screen. For example, you might want to try editing the program to read like this:
/* Program 1.2 Your Second C Program */
#include<stdio.h>
void main()
{
printf("If at first you don\'t succeed, try, try, try again!");
}The\'sequence in the middle of the text to be displayed is called an escape sequence. Here it’s a special way of including a single quote in the text. Because single quotes are used to indicate where a character constant begins and ends, you need a special way to indicate when you mean a single quote and not the start of a character constant. You’ll learn more about escapes sequences very soon. You can try recompiling the program, relinking it, and running it again once you’ve altered the source. With a following wind, and a bit of luck, you’ve now edited your first program. You’ve written a program using the editor, edited it, and then compiled, linked, and executed it.
Dealing with Errors To err is human, so there’s no need to be embarrassed about making mistakes. Fortunately, computers don’t generally make mistakes themselves and they’re actually very good at indicating where we’ve slipped up. Sooner or later your compiler is going to present you with a list (and sometimes a list that’s longer than you want) of the mistakes that are in your source code. You’ll usually get an indication of the statements that are in error. When this happens, you must return to the editing stage, find out what’s wrong with the incorrect code, and fix it. Keep in mind that one error can result in error messages for subsequent statements that may actually be correct. This usually happens with statements that refer to something that is supposed to be defined by a statement containing an error. Of course, if a statement that defines something has an error, then what was supposed to be defined won’t be.
Let’s step through what happens when your source code is incorrect by creating an error in a program. Edit your second program example, removing the semicolon (;) at the end of the line withprintf()in it, as shown here:
/* Program 1.2 Your Second C Program */ #include<stdio.h>
void main()
{
printf("If at first you don\'t succeed, try, try, try again!")
}
If you now try to compile this program, you’ll see an error message that will vary slightly depending on which compiler you’re using. A typical error message is as follows:
----------------------------------------------------------------------Syntax error : missing ';' before '}'
HELLO.C - 1 error(s), 0 warning(s)
----------------------------------------------------------------------
Here, the compiler is able to determine precisely what the error is, and where. There really should be a semicolon at the end of thatprintf()line. As you start writing your own programs, you’ll probably get lots of errors during compilation that are caused by simple punctuation mistakes. It’s so easy to forget a comma or a bracket, or to just press the wrong key. Don’t worry about this: lots of experienced programmers make exactly the same mistakes—even after years of practice.
As I said earlier, just one mistake can sometimes result in a whole stream of abuse from your compiler, as it throws you a multitude of different things that it doesn’t like. Don’t get put off by the number of errors reported. After you consider the messages carefully, the basic approach is to go back and edit your source code to fix what you can, ignoring the errors that you can’t understand. Then try to compile the source file again. With luck, you’ll get fewer errors the next time around.
To correct your example program, just go back to your editor and reenter the semicolon. Recompile and check for any other errors, and your program is fit to be run again.
Next: Dissecting a Simple Program >>
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 This article is excerpted from the book Beginning C, third edition, written by Ivor Horton (Apress, 2004; ISBN: 1590592530). Check it out today at your favorite bookstore. Buy this book now.
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