Instructions in c language

A program is a set of instructions. Instructions are also known as commands or statements. They are the sentences in program. Just like any other language C also provides variety of instructions.

Types of instructions

      Data type declaration instruction
Input/Output instruction
Arithmetic instruction
Control instruction 

Data type declaration instruction

From the list of keywords few are designed to use in declaration instruction. They are required to declare variables and functions. These keywords are

int, float, char, double, void

Here we are only concern with variable declaration. Declaration of functions will be deal in later chapter.

Consider the following statements

int x=5, y;

float k=2.34;

char a=’y’, ch;

These are examples of data type declaration instruction. Compiler when read these instructions, it would get aware of four things:

1)      Name of the variables

Here names are x ,y, k, a, ch

2)      Size of memory block

Size of int type block is 2 bytes, size of float block is 4 bytes, size of char block is 1 byte, size of double block is 8 bytes

3)      Type of content

int variable can contain integer constant, float and double variable can contain real constant and char variable can contain character constant.

4)      Value in variable

x contains 5, k contains 2.34 and a contains ‘y’.

Variables y and ch are not initialized but they are not empty. They contain unpredictable values which are of no use in the program, so called them garbage values.

Modifiers

Modifiers are the keywords used to modify the properties of data type.

Modifiers are short, long, signed, unsigned.

Here is the list of all possible combination of use of modifiers with data type:

Create variables to store integers:

  int,  short int, signed int, long int, unsigned int, unsigned short int, unsigned long int.

Create variables to store real constant

 float, double, long double

Create variables to store character constant

 char, unsigned char   

Modifiers affect size of data type (short and long), data range (signed and unsigned)

Following data type chart helps you to learn different properties modified in data type

   

Type	Size	Format specifier	Content  Type	Range
unsigned char	8 bits	%c	Character	0 to 255
Char	8 bits	%c	Character	-128 to 127
unsigned int	16 bits	%u	Integer	0 to 65,535
short int	16 bits	%d	Integer	-32,768 to 32,767
Int	16 bits	%d	Integer	-32,768 to 32,767
unsigned long	32 bits	%lu	Integer	0 to 4,294,967,295
Long	32 bits	%ld	Integer	-2,147,483,648 to 2,147,483,647
Float	32 bits	%f	Real	1.1754*(10^-38) to 3.4028* (10^+38)
Double	64 bits	%lf	Real	2.2250 * (10^-308) to 1.7976 * (10^+308)
long double	80 bits	%Lf	Real	3.4 * (10^-4932) to 1.1 * (10^4932)