This chapter is from the book
This chapter is from the book
This chapter is from the book
Kinds of Data
Your C programs must use data made up of numbers, characters, and words; programs process that data into meaningful information. Although many different kinds of data exist, the following three data types are by far the most common used in C programming:
- Characters
- Integers
- Floating points (also called real numbers)
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You might be yelling “How much math am I going to have to learn?! I didn’t think that was part of the bargain!” Well, you can relax, because C does your math for you; you don’t have to be able to add 2 and 2 to write C programs. You do, however, have to understand data types so that you will know how to choose the correct type when your program needs it.
Characters and C
A C character is any single character that your computer can represent. Your computer knows 256 different characters. Each of them is found in something called the ASCII table, located in Appendix A, “The ASCII Table.” (ASCII is pronounced askee. If you don’t know-ee, you can just ask-ee.) Anything your computer can represent can be a character. Any or all of the following can be considered characters:
A a 4 % Q ! + = ]
NOTE
The American National Standards Institute (ANSI), which developed ANSI C, also developed the code for the ASCII chart.
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Even the spacebar produces a character. Just as C needs to keep track of the letters of the alphabet, the digits, and all the other characters, it has to keep track of any blank spaces your program needs.
As you can see, every letter, number, and space is a character to C. Sure, a 4 looks like a number, and it sometimes is, but it is also a character. If you indicate that a particular 4 is a character, you can’t do math with it. If you indicate that another 4 is to be a number, you can do math with that 4. The same holds for the special symbols. The plus sign (+) is a character, but the plus sign also performs addition. (There I go, bringing math back into the conversation!)
All of C’s character data is enclosed in apostrophes ('). Some people call apostrophes single quotation marks. Apostrophes differentiate character data from other kinds of data, such as numbers and math symbols. For example, in a C program, all of the following are character data:
'A' 'a' '4' '%' ' ' '-'
None of the following can be character data because they have no apostrophes around them:
A a 4 % -
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None of the following are valid characters. Only single characters, not multiple characters, can go inside apostrophes.
- ‘C is fun’
- ‘C is hard’
- ‘I should be sailing!’
The first program in this chapter contains the character '\n'. At first, you might not think that \n is a single character, but it’s one of the few two-character combinations that C interprets as a single character. This will make more sense later.
If you need to specify more than one character (except for the special characters that you’ll learn, like the \n just described), enclose the characters in quotation marks ("). A group of multiple characters is called a string. The following is a C string:
“C is fun to learn.”
NOTE
That’s really all you need to know about characters and strings for now. In Chapters 4 through 6, you’ll learn how to use them in programs. When you see how to store characters in variables, you’ll see why the apostrophe and quotation marks are important.
Numbers in C
Although you might not have thought about it before now, numbers take on many different sizes and shapes. Your C program must have a way to store numbers, no matter what the numbers look like. You must store numbers in numeric variables. Before you look at variables, a review of the kinds of numbers will help.
Whole numbers are called integers. Integers have no decimal points. (Remember this rule: Like most reality shows, integers have no point whatsoever.) Any number without a decimal point is an integer. All of the following are integers:
10 54 0 –121 –68 752
WARNING
Never begin an integer with a leading 0 (unless the number is zero), or C will think you typed the number in hexadecimal or octal. Hexadecimal and octal, sometimes called base-16 and base-8, respectively, are weird ways of representing numbers. 053 is an octal number, and 0x45 is a hexadecimal number. If you don’t know what all that means, just remember for now that C puts a hex on you if you mess around with leading zeroes before integers.
Numbers with decimal points are called floating-point numbers. All of the following are floating-point numbers:
547.43 0.0 0.44384 9.1923 –168.470 .22
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As you can see, leading zeroes are okay in front of floating-point numbers.
The choice of using integers or floating-point numbers depends on the data your programs are working with. Some values (such as ages and quantities) need only integers; other values (such as money amounts or weights) need the exact amounts floating-point numbers can provide. Internally, C stores integers differently than floating-point values. As you can see from Figure 2.2, a floating-point value usually takes twice as much memory as an integer. Therefore, if you can get away with using integers, do so—save floating points for values that need the decimal point.
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FIGURE 2.2. Storing floating-point values often takes more memory than integers.
NOTE
Figure 2.2 shows you that integers generally take less memory than floating-point values, no matter how large or small the values stored there are. On any given day, a large post office box might get much less mail than a smaller one. The contents of the box don’t affect what the box is capable of holding. The size of C’s number storage is affected not by the value of the number, but by the type of the number.
Different C compilers use different amounts of storage for integers and floating-point values. As you will learn later, there are ways of finding out exactly how much memory your C compiler uses for each type of data.