There are a number of operators available including addition, ‘+’, subtraction, ‘-‘, division ‘/’, and multiplication ‘*’. By definition, an expression, in C, is an interpreted combination of values, variables, operators or functions. To manipulate the variable, ‘a’, declared and defined in the previous section, an expression is needed. RASE, i.e., register, auto, static, and extern.Įxample: the arithmetic mean of two numbers īorland Turbo-C (Linux/Unix users may need Linux implementation of conio.h):

Storage classes can be remembered easily by remembering mnemonic For function declarations, the storage class extern can be omitted. extern - this storage class specifier is used to declare a variable or function that is defined in another module.Thus even though it is a global variable, it can not be accessed from another module (it is said to have internal linkage).

For global variables and functions: When a global variable or a function is defined as static, its scope is reduced to the C program file in which it is defined.

A static variable in a function definition will retain its value across multiple calls to the function.

For local variables: when a local variable is defined with the static storage class specifier, it is initialized to 0 by default in the absence of an explicit initialisation value.

static - this storage class specifier is used for two main purposes as given below.

However, defining a variable with this specifier does not guarantee that it will be stored in a CPU register (a compiler can ignore it) and modern compilers should allocate registers much better than a programmer can.

register: this storage class specifier can be used to indicate to the compiler that the variable will be used frequently and it should be placed in a CPU register, if possible.

Use of auto is archaic and there is no need to use it. auto variables contain garbage until explicitly initialised. Variables declared auto will automatically have their storage allocated on entry to a function and deallocated when the function exits.

auto: this is the default storage class specifier for variables defined inside a function.

There are several storage class specifiers: There are two types of storage classes: automatic and static. Storage classes define the longevity and scope of variables and functions. Note: a Standard conforming compiler can ignore these qualifiers nevertheless, it must issue a message when an attempt is made to alter an object declared as const. volatile - the volatile qualifier indicates that variable values can be changed without the current program's knowledge and so the compiler should not optimize away uses of that variable.As an alternative, the #define preprocessor directive can be used to define constant values and these will consume no memory space. const - the const qualifier is used to indicate the variable value can not be changed after its initialization.Note that the values given are acceptable minimum magnitudes defined by the C Standard - each implementation will define values greater or equal in magnitude.Ĭ type qualifiers add special properties to the variables being declared. Using these qualifiers, basic data types can be flavoured in many ways as shown in the table below. unsigned (applied to char, or any integer).signed (applied to char, or any integer).Qualifiers available in the C language are: Qualifiers are used to make variable declaration more specific to variable uses. In addition to basic data types C also defines certain qualifiers to these data types. double - double-precision floating point.float - single-precision floating point.int - an integer reflects size of integers on host machine.When a variable is defined, a memory location will be assigned to the newly defined variable and it will also define the type of data that memory location will hold. Data types indicate the type of data a variable can hold. Int x = 1 Data Types and Qualifiers Ĭ is strongly typed, which means that variables must be explicitly assigned a data type.

Basic data types in c