Each program must have a starting point. When you run a program, DOS sends it off on its way — like launching a ship. As its last dock-master duty, DOS hurls the microprocessor headlong into the program. The microprocessor then takes the program's helm at that specific starting point.
In all C programs, the starting point is the main() function. Every C program has one, even GOODBYE.C (shown in Figure 1). The main() function is the engine that makes the program work, which displays the message on the screen.
Other C programs may carry out other tasks in their main() function. But whatever's there, it's the first instruction given to the computer when the program runs.
- main() is the name given to the first (or primary) function in every C program. C programs can have other functions, but main() is the first one.
- It's a common convention to follow a C language function name with parentheses, as in main(). It doesn't mean anything. Everyone does it, and it's included here so that you don't freak when you see it elsewhere.
- In Borland C++, you may have seen the error message say "in function main." This message refers to the main function — the void main() thing that contains the C language instructions you've been writing.
- A function is a machine — it's a set of instructions that does something. C programs can have many functions in them, though the main function is the first function in a C program. It's required.
Function. Get used to that word.
Pieces' parts
Here are some interesting pieces of the C program shown in Figure 1:
1. #include is known as a preprocessor directive, which sounds impressive, and it may not be the correct term, but you're not required to memorize it anyhow. What it does is tell the compiler to "include" another program or file along with your source code, which generally avoids a lot of little, annoying errors that would otherwise occur.
2.
3. void main identifies the name of the function main. The void identifies the type of function or what the function produces. In the case of main, it doesn't produce anything, and the C term for that is "void."
4. Two empty parentheses follow the function name. Sometimes, there may be items in these parentheses.
5. The curly brackets or braces enclose the function, hugging in tight all its parts. Everything between { and } is part of the function main() in Figure 1.
6. printf is a C language instruction, part of the programming language that eventually tells the computer what to do.
7. Belonging to printf are more parentheses. In this case, the parentheses enclose text, or a "string" of text. Everything between the double quotes (") is part of printf's text string.
8. An interesting part of the text string is n. That's the backslash character and a little n. What it represents is the character produced by pressing the Enter key. What it does is to end the text string with a "new line."
9. Finally, the printf line, or statement, ends with a semicolon. The semicolon is how the C compiler knows when one statement ends and another begins — like a period at the end of a sentence. Even though printf is the only instruction in this program, the semicolon is still required.
• Text in a program is referred to as a string. For example, "la-de-da" is a string of text. The string is enclosed by double quotes.
• The C language is composed of keywords that appear in statements. The statements end in semicolons, just as sentences in English end in periods.)
The C language itself — the keywords
The C language is really rather brief. There are only 33 keywords in C. If only French were that easy! Table 1 shows the keywords that make up the C language.
Table 1: C Language Keywords
asm | enum | signed |
auto | extern | sizeof |
break | float | static |
case | for | struct |
char | goto | switch |
const | if | typedef |
continue | int | union |
default | long | unsigned |
do | register | void |
double | return | volatile |
else | short | while |
Not bad, eh? But these aren't all the words you find in the C language. Other words or instructions are called functions. These include jewels like printf and several dozen other common functions that assist the basic C language keywords in creating programs.
If you're using DOS, additional functions specific to DOS are piled on top of the standard C armada of functions. And if you get into Windows, you find hoards of Windows-specific functions that bring C's full vocabulary into the hundreds. And no, you don't really have to memorize any of them. This is why all C compilers come with a language reference, which you'll undoubtedly keep close to your PC's glowing bosom.
Languages are more than a collection of words. They also involve grammar, or properly sticking together the words so that understandable ideas are conveyed. This concept is completely beyond the grasp of the modern legal community.
In addition to grammar, languages require rules, exceptions, jots and tittles, and all sorts of fun and havoc. Programming languages are similar to spoken language in that they have various parts and lots of rules.
- You will never be required to memorize the 33 keywords.
- In fact, of the 33 keywords, you may end up using only half on a regular basis.
- Some of the keywords are real words! Others are abbreviations or combinations of two or more words. Still others are cryptograms of the programmer's girlfriends' names.
- Each of the keywords has its own set of problems. You don't just use the keyword else, for example; you must use it in context.
- Functions like printf require a set of parentheses and lots of stuff inside the parentheses. (Don't fret over this right now; just nod your head and smile in agreement, "Yes, printf does require lots of stuff.")
- By the way, the fact that printf is a C function and not a keyword is why the #include
thing is required at the beginning of a program. The STDIO.H file contains the instructions telling the compiler what exactly printf is and does. If you edit out the #include line, the compiler produces a funky "I don't know that printf thing" type of error.
