c language

SELECTION STATEMENT: if

Selection Statements

Selection statements change the flow of program execution by evaluating the result of an expression, referred to as a condition. The if and switch statements are selection statements.

if Statement

An if statement evaluates a condition and executes its associated statement if the condition is true. Otherwise it skips the statement and processing continues on to the next statement following the if.


Figure 6-1: if Statement Diagram
Figure 6-1 illustrates the if statement. The expression that formulates the condition must evaluate to either true or false. True is any non-zero integer value.

if-else Statement

The if-else statement works like the if statement with one major difference. If the condition evaluates to false the statement following the else keyword will execute. A diagram of the if-else statement is shown in Figure 6-2.


Figure 6-2: if-else Statement Diagram

Monday, 5 November 2012

DATA TYPES IN C

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.

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.

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.