2.Introduction to data types in C
The C programming language is a "middle-level" language. It provides low-level programming capability at the expense of some user-friendliness. Cynics tend to claim that C combines the flexibility and power of assembly language with the user-friendliness of high-level language, but experience programmers find that the limited set of keywords and the use of pointers allows for fast and elegant programming solutions. C first rose to popularity with the growth of UNIX, and has been used creating the Windows operating sytem from its earliest versions. It is also used in microcontrollers and super-computers.The original implementations of C were defined as described in the classic reference,
Variables in C Programming
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Like most programming languages, C is able to use and process named variables and their contents. Variables are simply names used to refer to some location in memory – a location that holds a value with which we are working.It may help to think of variables as a placeholder for a value. You can think of a variable as being equivalent to its assigned value. So, if you have a variable i that is initialized (set equal) to 4, then it follows that i+1 will equal 5.Since C is a relatively low-level programming language, before a C program can utilize memory to store a variable it must claim the memory needed to store the values for a variable. This is done by declaring variables. Declaring variables is the way in which a C program shows the number of variables it needs, what they are going to be named, and how much memory they will need.Within the C programming language, when managing and working with variables, it is important to know the type of variables and the size of these types. Since C is a fairly low-level programming language, these aspects of its working can be hardware specific – that is, how the language is made to work on one type of machine can be different from how it is made to work on another.All variables in C are typed. That is, every variable declared must be assigned as a certain type of variable.
Basic Data Types in C
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In Standard C there are four basic data types. They are int, char, float, and double.
integer type
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The int type stores integers in the form of "whole numbers". An integer is typically the size of one machine word, which on most modern home PCs is 32 bits (4 octets). Examples of literals are whole numbers (integers) such as 1,2,3, 10, 100... When int is 32 bits (4 octets), it can store any whole number (integer) between -2147483648 and 2147483647. A 32 bit word (number) has the possibility of representing any one number out of 4294967296 possibilities (2 to the power of 32).
The Float Data Type
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float is short for floating point. It stores real numbers also, but is only one machine word in size. Therefore, it is used when less precision than a double provides is required. float literals must be suffixed with F or f, otherwise they will be interpreted as doubles. Examples are: 3.1415926f, 4.0f, 6.022e+23f. float variables can be declared using the float keyword.
The Double Data Type
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The double and float types are very similar. The float type allows you to store single-precision floating point numbers, while the double keyword allows you to store double-precision floating point numbers – real numbers, in other words, both integer and non-integer values. Its size is typically two machine words, or 8 bytes on most machines. Examples of double literals are 3.1415926535897932, 4.0, 6.022e+23 (scientific notation). If you use 4 instead of 4.0, the 4 will be interpreted as an int.
The distinction between floats and doubles was made because of the differing sizes of the two types. When C was first used, space was at a minimum and so the judicious use of a float instead of a double saved some memory. Nowadays, with memory more freely available, you do not really need to conserve memory like this – it may be better to use doubles consistently. Indeed, some C implementations use doubles instead of floats when you declare a float variable.
The char type
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The char type is capable of holding any member of the execution character set. It stores the same kind of data as an int (i.e. integers), but typically has a size of one byte. The size of a byte is specified by the macro CHAR_BIT which specifies the number of bits in a char (byte). In standard C it never can be less than 8 bits. A variable of type char is most often used to store character data, hence its name. Most implementations use the ASCII character set as the execution character set, but it's best not to know or care about that unless the actual values are important.
Examples of character literals are 'a', 'b', '1', etc., as well as some special characters such as '\0' (the null character) and '\n' (newline, recall "Hello, World"). Note that the char value must be enclosed within single quotations.