Chapter 1 - Getting Started WHAT IS AN IDENTIFIER? Before you can do anything in any language, you must at least know how to name an identifier. An identifier is used for any variable, function, data definition, etc. In the programming language C, an identifier is a combination of alphanumeric characters, the first being a letter of the alphabet or an underline, and the remaining being any letter of the alphabet, any numeric digit, or the underline. In the case of some compilers, a dollar sign is permitted but not as the first character of an identifier. It should be pointed out that even though a dollar sign may be permitted by your C compiler, it is not used anywhere in this tutorial since it is not in general use by C programmers, and is not even allowed by most compilers. If you do not plan to write any portable code, you can use it at will if you feel it makes your code more readable. Two rules must be kept in mind when naming identifiers. 1. The case of alphabetic characters is significant. Using "INDEX" for a variable is not the same as using "index" and neither of them is the same as using "InDeX" for a variable. All three refer to different variables. 2. As C is defined, up to 32 significant characters can be used and will be considered significant by most compilers. If more than 32 are used, they will be ignored by the compiler. WHAT ABOUT THE UNDERLINE? Even though the underline can be used as part of a variable name, and adds greatly to the readability of the resulting code, it seems to be used very little by experienced C programmers. It adds greatly to the readability of a program to use descriptive names for variables and it would be to your advantage to do so. Pascal programmers tend to use long descriptive names, but most C programmers tend to use short cryptic names. Most of the example programs in this tutorial use very short names for that reason. Any computer program has two entities to consider, the data, and the program. They are highly dependent on one another and careful planning of both will lead to a well planned and well written program. Unfortunately, it is not possible to study either completely without a good working knowledge of the other. For this reason, this tutorial will jump back and forth between teaching methods of program Page 3 Chapter 1 - Getting Started writing and methods of data definition. Simply follow along and you will have a good understanding of both. Keep in mind that, even though it seems expedient to sometimes jump right into the program coding, time spent planning the data structures will be well spent and the final program will reflect the original planning. HOW THIS TUTORIAL IS WRITTEN As you go through the example programs, you will find that every program is complete. There are no program fragments that could be confusing. This allows you to see every requirement that is needed to use any of the features of C as they are presented. Some tutorials I have seen give very few, and very complex examples. They really serve more to confuse the student. This tutorial is the complete opposite because it strives to cover each new aspect of programming in as simple a context as possible. This method, however, leads to a lack of knowledge in how the various parts are combined. For that reason, the last chapter is devoted entirely to using the features taught in the earlier chapters. It will illustrate how to put the various features together to create a usable program. They are given for your study, and are not completely explained. Enough details of their operation are given to allow you to understand how they work after you have completed all of the previous lessons. At this point, you should load and run FIRSTEX.C if you have not yet done so, to see that your C compiler is properly loaded and operating. If you have any problems, the COMPILER.DOC file may have help for your compiler. Even if it doesn't have help for your particular compiler, the notes on another compiler may be helpful for yours since C compilers tend to have many things in common. A DISCUSSION OF SOME OF THE FILES CCL.BAT This file, which does not exist on the distribution disk, is the batch file that calls in an editor, then the compiler (pass 1 and pass 2, if it exists), and finally runs the resulting compiled program. There are several examples of batch files which can be used with various compilers given in the "COMPILER.DOC" file on the distribution diskette. It is up to you to type in a batch file for use with your particular compiler, considering also the method required to call in your editor. To use it, simply type the batchfile name with the desired filename. After typing in your particular CCL.BAT file, try it by typing CCL FIRSTEX. Page 4 Chapter 1 - Getting Started You will get the sourcefile displayed on the monitor by your editor. If you don't have one of the compilers listed in the "COMPILER.DOC" file, you will have to modify the batch file to accomodate your compiler. Note that if you are using Turbo C, you can use the Integrated Environment and you will not need a batch file. The same is true if you are using Microsoft Quick-C, it has its own built in operating environment so you will not need a batchfile. If you have a hard disk available, it will be up to you to modify the batch file to use the hard disk. Note that most of the batch files have statements to erase the object files and executable files after use to prevent the disk from filling up with unecessary files after a program has served its purpose. Even though you will have a lot of files to compile and run, you will find that a suitable batch file will help you to get through the steps quickly and with little typing. LIST.EXE This file will list the source files for you with line numbers and filename. To use it, simply type "LIST" followed by the appropriate filename. Type LIST FIRSTEX.C now for an example. The C source code is given later in Chapter 14 along with a brief description of its operation. After you have completed your study of C, you will have the ability to read and understand the source code for this program. PRINTALL.BAT This is a batch file that will call the above LIST.EXE file once for each of the example C programs, printing all of the files out. If you want a hardcopy of all of the files, enter PRINTALL and watch as your printer fills about 150 sheets of paper with C programs. Page 5