122 Part II: Run and Scream from Variables and Math

Single-character variables

Like a string of text, the single-character variable is declared by using the char keyword. Unlike a string, the single-character variable holds only one character — no more. In a way, the character variable is like a padded cell. The string variable is merely several padded cells one after the other — like an asylum.

The char keyword is used to set aside storage space for a single-character variable. Here’s the format:

char var;

char is written in lowercase, followed by a space and then var, the name of the variable to be created.

In the following format, you can predefine a single-character value:

char var=’c’;

Typing those hard-to-reach characters

Some characters can’t be typed at the keyboard or entered by using escape sequences. For example, the extended ASCII characters used on most PCs — which include the line-drawing characters, math symbols, and some foreign characters — require some extra effort to stuff into character variables. It’s possible — just a little technical. Follow these steps:

1.Look up the character’s secret code value — its ASCII or extended ASCII code number.

2.Convert that code number into base 16, the hexadecimal, or “hex,” system. (That’s why hexadecimal values are usually shown in the ASCII tables and charts.)

3.Specify that hex value, which is two digits long, after the \x escape sequence.

4.Remember to enclose the entire escape sequence — four characters long — in single quotes.

Suppose that you want to use the British pound symbol, £, in your program. That character’s secret code number is 156. Look it up in Appendix B. You can see that the hexadecimal value is 9C. (Hex numbers contain letters.) So you specify the following escape sequence in your program:

‘\x9C’

Notice that it’s enclosed in single quotes. The C, or any other hexadecimal letter, can be upperor lowercase. When the escape sequence is assigned to a character variable, the C compiler takes the preceding number and converts it into a character — the £ — which sits snugly until needed.

Chapter 10: Cook That C Variable Charred, Please 123

char is followed by a space. The name of the variable you’re creating, var, is followed by an equal sign and then a character in single quotes. The statement ends in a semicolon.

Inside the single quotes is a single character, which is assigned to the vari­ able var. You can specify any single character or use one of the escape sequences to specify a nontypable character, such as a double-quote, a single quote, or the Enter key press. (See Table 24-1 in Chapter 24 for the full list of escape sequences; also see the nearby sidebar, “Typing those hard-to- reach characters.”)

The single-character variable is ideal for reading one character (obviously) from the keyboard. By using miracles of the C language not yet known, you can compare that character with other characters and make your programs do wondrous things. This is how a menu system works, how you can type single-key commands without having to press Enter, and how you can write your own keyboard-reading programs. Oh, it can be fun.

Char in action

The following statement creates the character variable ch for use in the pro­ gram (you can also predefine the variable if need be):

char ch;

This next statement creates the character variable x and assigns to it the char­ acter value ‘X’ (big X):

char x=’X’;

When you assign a character to a single-character variable, you use single quotes. It’s a must!

Some characters, you can’t really type at the keyboard. For example, to pre­ define a variable and stick the Tab key into it, you use an escape sequence:

char tab=’\t’;

This statement creates the character variable tab and places in that variable the tab character, represented by the \t escape sequence.

Single-character variables are created by using the char keyword.

Don’t use the square brackets when you’re declaring single-character variables.

124 Part II: Run and Scream from Variables and Math

If you predefine the variable’s value with a character, enclose that char­ acter in single quotes. Don’t use double quotes.

You can assign almost any character value to the character variable. Special, weird, and other characters can be assigned by using the escape sequences.

Information about creating string variables is presented in Chapter 4. This chapter deals primarily with single-character variables.

Stuffing characters into character variables

You can assign a character variable a value in one of several ways. The first way is to just stuff a character in there, similar to the way you stuff a value into a numeric variable or your foot into a sock. If key is a character variable, for example, you can place the character ‘T’ in it with this statement:

key=’T’;

The T, which must be in single quotes, ladies and gentlemen, slides through the equal sign and into the key variable’s single-character holding bin. The statement ends in a semicolon. (I assume that key was defined as a character variable by using the char key; statement, earlier in the program.)

In addition to single characters, you can specify various escape sequences (the \-character things), values, and whatnot. As long as it’s only one charac­ ter long, you’re hunky-dory.

Another way to stick a character into a single-character variable is to slide one from another character variable. Suppose that both old and new are charac­ ter variables. The following is acceptable:

old=new;

The character in new squirts through the equal sign and lands in the charac­ ter variable old. After the preceding statement, both variables hold the same character. (It’s a copy operation, not a move.)

You can assign single characters to single-character variables. But. . . .

You still cannot use the equal sign to put a string of text into a string variable. Sorry. It just can’t be done.