C DATA TYPES

C DATA TYPESIn the C programming language, data types refers to an extensive system for declaring variables of different types. The language itself provides basic arithmetic types and syntax to build array and compound types. Several headers in the standard library contain definitions of support types, that have additional properties, such as exact size, guaranteed In the C programming language, data types refers to an extensive system used for declaring variables or functions of different types. The type of a variable determines how much space it occupies in storage and how the bit pattern stored is interpreted. The types in C can be classified as follows: S.N. Types and Description 1 Basic Types: They are arithmetic types and consists of the two types: (a) integer types and (b) floating-point types. 2 Enumerated types: They are again arithmetic types and they are used to define variables that can only be assigned certain discrete integer values throughout the program. 3 The type void: The type specifier void indicates that no value is available. 4 Derived types: They include (a) Pointer types, (b) Array types, (c) Structure types, (d) Union types and (e) Function types. The array types and structure types are referred to collectively as the aggregate types. The type of a function specifies the type of the function's return value. We will see basic types in the following section where as other types will be covered in the upcoming chapters. Integer Types Following table gives you detail about standard integer types with its storage sizes and value ranges: Type Storage size Value range char 1 byte -128 to 127 or 0 to 255 unsigned char 1 byte 0 to 255 signed char 1 byte -128 to 127 int 2 or 4 bytes -32,768 to 32,767 or -2,147,483,648 to 2,147,483,647 unsigned int 2 or 4 bytes 0 to 65,535 or 0 to 4,294,967,295 short 2 bytes -32,768 to 32,767 unsigned short 2 bytes 0 to 65,535 long 4 bytes -2,147,483,648 to 2,147,483,647 unsigned long 4 bytes 0 to 4,294,967,295 To get the exact size of a type or a variable on a particular platform, you can use the sizeof operator. The expressions sizeof(type) yields the storage size of the object or type in bytes. Following is an example to get the size of int type on any machine: #include #include int main() { printf("Storage size for int : %d \n", sizeof(int)); return 0; }When you compile and execute the above program it produces following result on Linux: Storage size for int : 4 Floating-Point Types Following table gives you detail about standard float-point types with storage sizes and value ranges and their precision: Type Storage size Value range Precision float 4 byte 1.2E-38 to 3.4E+38 6 decimal places double 8 byte 2.3E-308 to 1.7E+308 15 decimal places long double 10 byte 3.4E-4932 to 1.1E+4932 19 decimal places The header file float.h defines macros that allow you to use these values and other details about the binary representation of real numbers in your programs. Following example will print storage space taken by a float type and its range values: #include #include int main() { printf("Storage size for float : %d \n", sizeof(float)); printf("Minimum float positive value: %E\n", FLT_MIN ); printf("Maximum float positive value: %E\n", FLT_MAX ); printf("Precision value: %d\n", FLT_DIG ); return 0; }When you compile and execute the above program it produces following result on Linux: Storage size for float : 4 Minimum float positive value: 1.175494E-38 Maximum float positive value: 3.402823E+38 Precision value: 6 The void Type The void type specifies that no value is available. It is used in three kinds of situations: S.N. Types and Description 1 Function returns as void There are various functions in C who do not return value or you can say they return void. A function with no return value has the return type as void. For example void exit (int status); 2 Function arguments as void There are various functions in C who do not accept any parameter. A function with no parameter can accept as a void. For example int rand(void); 3 Pointers to void A pointer of type void * represents the address of an object, but not its type. For example a memory allocation function void *malloc( size_t size ); returns a pointer to void which can be casted to any data type. The void type may not be understood to you at this point, so let us proceed and we will cover these concepts in upcoming chapters. A variable is nothing but a name given to a storage area that our programs can manipulate. Each variable in C has a specific type, which determines the size and layout of the variable's memory; the range of values that can be stored within that memory; and the set of operations that can be applied to the variable. The name of a variable can be composed of letters, digits, and the underscore character. It must begin with either a letter or an underscore. Upper and lowercase letters are distinct because C is case-sensitive. Based on the basic types explained in previous chapter, there will be following basic variable types: Type Description char Typically a single octet(one byte). This is an integer type. int The most natural size of integer for the machine. float A single-precision floating point value. double A double-precision floating point value. void Represents the absence of type. C programming language also allows to define various other type of variables which we will cover in subsequent chapters like Enumeration, Pointer, Array, Structure, Union etc. For this chapter, let us study only basic variable types. Variable Declaration in C All variables must be declared before we use them in C program, although certain declarations can be made implicitly by content. A declaration specifies a type, and contains a list of one or more variables of that type as follows: type variable_list;Here, type must be a valid C data type including char, int, float, double, or any user defined data type etc., and variable_list may consist of one or more identifier names separated by commas. Some valid variable declarations along with their definition are shown here: int i, j, k; char c, ch; float f, salary; double d;You can initialize a variable at the time of declaration as follows: int i = 100;An extern declaration is not a definition and does not allocate storage. In effect, it claims that a definition of the variable exists some where else in the program. A variable can be declared multiple times in a program, but it must be defined only once. Following is the declaration of a variable with extern keyword: extern int i;Though you can declare a variable multiple times in C program but it can be decalred only once in a file, a function or a block of code. Variable Initialization in C Variables are initialized (assigned an value) with an equal sign followed by a constant expression. The general form of initialization is: variable_name = value;Variables can be initialized (assigned an initial value) in their declaration. The initializer consists of an equal sign followed by a constant expression as follows: type variable_name = value;Some examples are: int d = 3, f = 5; /* initializing d and f. */ byte z = 22; /* initializes z. */ double pi = 3.14159; /* declares an approximation of pi. */ char x = 'x'; /* the variable x has the value 'x'. */It is a good programming practice to initialize variables properly otherwise, sometime program would produce unexpected result. Try following example which makes use of various types of variables: #include int main () { /* variable declaration: */ int a, b; int c; float f; /* actual initialization */ a = 10; b = 20; c = a + b; printf("value of c : %d \n", c); f = 70.0/3.0; printf("value of f : %f \n", f); return 0; }When the above code is compiled and executed, it produces following result: value of c : 30 value of f : 23.333334 Lvalues and Rvalues in C: There are two kinds of expressions in C: 1.lvalue : An expression that is an lvalue may appear as either the left-hand or right-hand side of an assignment. 2.rvalue : An expression that is an rvalue may appear on the right- but not left-hand side of an assignment. Variables are lvalues and so may appear on the left-hand side of an assignment. Numeric literals are rvalues and so may not be assigned and can not appear on the left-hand side. Following is a valid statement: int g = 20;But following is not a valid statement and would generate compile-time error: 10 = 20; The constants refer to fixed values that the program may not alter during its execution. These fixed values are also called literals. Constants can be of any of the basic data types like an integer constant, a floating constant, a character constant, or a string literal. There are also enumeration constants as well. The constants are treated just like regular variables except that their values cannot be modified after their definition. Integer literals An integer literal can be a decimal, octal, or hexadecimal constant. A prefix specifies the base or radix: 0x or 0X for hexadecimal, 0 for octal, and nothing for decimal. An integer literal can also have a suffix that is a combination of U and L, for unsigned and long, respectively. The suffix can be uppercase or lowercase and can be in any order. Here are some examples of integer literals: 212 /* Legal */ 215u /* Legal */ 0xFeeL /* Legal */ 078 /* Illegal: 8 is not an octal digit */ 032UU /* Illegal: cannot repeat a suffix */Following are other examples of various type of Integer literals: 85 /* decimal */ 0213 /* octal */ 0x4b /* hexadecimal */ 30 /* int */ 30u /* unsigned int */ 30l /* long */ 30ul /* unsigned long */Floating-point literals A floating-point literal has an integer part, a decimal point, a fractional part, and an exponent part. You can represent floating point literals either in decimal form or exponential form. While representing using decimal form, you must include the decimal point, the exponent, or both and while representing using exponential form, you must include the integer part, the fractional part, or both. The signed exponent is introduced by e or E. Here are some examples of floating-point literals: 3.14159 /* Legal */ 314159E-5L /* Legal */ 510E /* Illegal: incomplete exponent */ 210f /* Illegal: no decimal or exponent */ .e55 /* Illegal: missing integer or fraction */Character constants Character literals are enclosed in single quotes e.g., 'x' and can be stored in a simple variable of char type. A character literal can be a plain character (e.g., 'x'), an escape sequence (e.g., '\t'), or a universal character (e.g., '\u02C0'). There are certain characters in C when they are proceeded by a back slash they will have special meaning and they are used to represent like newline (\n) or tab (\t). Here you have a list of some of such escape sequence codes: Escape sequence Meaning \\ \ character \' ' character \" " character \? ? character \a Alert or bell \b Backspace \f Form feed \n Newline \r Carriage return \t Horizontal tab \v Vertical tab \ooo Octal number of one to three digits \xhh . . . Hexadecimal number of one or more digits Following is the example to show few escape sequence characters: #include int main() { printf("Hello\tWorld\n\n"); return 0; }When the above code is compiled and executed, it produces following result: Hello World String literals String literals or constants are enclosed in double quotes "". A string contains characters that are similar to character literals: plain characters, escape sequences, and universal characters. You can break a long lines into multiple lines using string literals and separating them using whitespaces. Here are some examples of string literals. All the three forms are identical strings. "hello, dear" "hello, \ dear" "hello, " "d" "ear"Defining Constants There are two simple ways in C to define constants: 1.Using #define preprocessor. 2.Using const keyword. The #define Preprocessor Following is the form to use #define preprocessor to define a constant: #define identifier valueFollowing example explains it in detail: #include #define LENGTH 10 #define WIDTH 5 #define NEWLINE '\n' int main() { int area; area = LENGTH * WIDTH; printf("value of area : %d", area); printf("%c", NEWLINE); return 0; }When the above code is compiled and executed, it produces following result: value of area : 50 The const Keyword You can use const prefix to declare constants with a specific type as follows: const type variable = value;Following example explains it in detail: #include int main() { const int LENGTH = 10; const int WIDTH = 5; const char NEWLINE = '\n'; int area; area = LENGTH * WIDTH; printf("value of area : %d", area); printf("%c", NEWLINE); return 0; }When the above code is compiled and executed, it produces following result: value of area : 50 Note that it is a good programming practice to define constants in CAPITALS. A storage class defines the scope (visibility) and life time of variables and/or functions within a C Program. These specifiers precede the type that they modify. There are following storage classes which can be used in a C Program auto register static extern The auto Storage Class The auto storage class is the default storage class for all local variables. { int mount; auto int month; }The example above defines two variables with the same storage class, auto can only be used within functions, i.e. local variables. The register Storage Class The register storage class is used to define local variables that should be stored in a register instead of RAM. This means that the variable has a maximum size equal to the register size (usually one word) and can't have the unary '&' operator applied to it (as it does not have a memory location). { register int miles; }The register should only be used for variables that require quick access such as counters. It should also be noted that defining 'register' goes not mean that the variable will be stored in a register. It means that it MIGHT be stored in a register depending on hardware and implementation restrictions. The static Storage Class The static storage class instructs the compiler to keep a local variable in existence during the lifetime of the program instead of creating and destroying it each time it comes into and goes out of scope. Therefore, making local variables static allows them to maintain their values between function calls. The static modifier may also be applied to global variables. When this is done, it causes that variable's scope to be restricted to the file in which it is declared. In C programming, when static is used on a class data member, it causes only one copy of that member to be shared by all objects of its class. #include /* function declaration */ void func(void); static int count = 5; /* global variable */ main() { while(count--) { func(); } return 0; } /* function definition */ void func( void ) { static int i = 5; /* local static variable */ i++; printf("i is %d and count is %d\n", i, count); }You may not understand this example at this time because I have used function and global variables which I have not explained so far. So for now let us proceed even if you do not understand it completely. When the above code is compiled and executed, it produces following result: i is 6 and count is 4 i is 7 and count is 3 i is 8 and count is 2 i is 9 and count is 1 i is 10 and count is 0 The extern Storage Class The extern storage class is used to give a reference of a global variable that is visible to ALL the program files. When you use 'extern' the variable cannot be initialized as all it does is point the variable name at a storage location that has been previously defined. When you have multiple files and you define a global variable or function which will be used in other files also, then extern will be used in another file to give reference of defined variable or function. Just for understanding extern is used to declare a global variable or function in another files. The extern modifier is most commonly used when there are two or more files sharing the same global variables or functions as explained below. First File: main.c #include int count ; extern void write_extern(); main() { count = 5; write_extern(); }Second File: support.c #include extern int count; void write_extern(void) { printf("count is %d\n", count); }Here extern keyword is being used to declare count in the second file where as it has its definition in the first file main.c. Now compile these two files as follows: $gcc main.c support.cThis will produce a.out executable program, when this program is executed, it produces following result: An operator is a symbol that tells the compiler to perform specific mathematical or logical manipulations. C language is rich in built-in operators and provides following type of operators: Arithmetic Operators Relational Operators Logical Operators Bitwise Operators Assignment Operators Misc Operators This tutorial will explain the arithmetic, relational, and logical, bitwise, assignment and other operators one by one. Arithmetic Operators Following table shows all the arithmetic operators supported by C language. Assume variable A holds 10 and variable B holds 20 then: Show Examples Operator Description Example + Adds two operands A + B will give 30 - Subtracts second operand from the first A - B will give -10 * Multiply both operands A * B will give 200 / Divide numerator by de-numerator B / A will give 2 % Modulus Operator and remainder of after an integer division B % A will give 0 ++ Increment operator increases integer value by one A++ will give 11 -- Decrement operator decreases integer value by one A-- will give 9 Relational Operators Following table shows all the relational operators supported by C language. Assume variable A holds 10 and variable B holds 20 then: Show Examples Operator Description Example == Checks if the value of two operands is equal or not, if yes then condition becomes true. (A == B) is not true. != Checks if the value of two operands is equal or not, if values are not equal then condition becomes true. (A != B) is true. > Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true. < Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true. >= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true. <= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.