Chapter 3

 Data types

In C, each variable must be declared before it is used. When a variable is declared, a type is assigned to it. During compilation, memory is reserved for each variable. The amount of memory that is reserved depends on the stated type.

The memory requirements for each data type will determine the permissible range of values for that data type.

 

 

Data Types                                          Memory Req                               Range

1. char (signed)                                   1  byte                                     -128  to 127

    Unsigned char                                 1 byte                                        0 to 255

 

2.  int                                                   2 bytes

    Signed int                                        2 bytes                                    -32768 to 32767

    Unsigned int                                   2 bytes                                    0 to 65535

    Long int                                          4 bytes                                    0 to 2 ³²-1

 

3. float                                                4 bytes                                    -3.4e^-38 to 3.4e³⁸

 

4. double                                             8 bytes                                    1.7e^-308 to 1.7e³⁰⁸

 

 

 

Format Specifier

 

c          data item in a single character

d          data item in an integer

e          data item in a floating point value in exponent form

f           data item in floating point value

g          data item is a floating point value without trialing zeros

h          data item is a short integer

i           data item is a signed integer

ld         data item is a long integer

o          data item is an octal integer

x          data item is a hexadecimal integer

s          data item is a string

u          data item is unsigned integer

           

# modifying the basic data types

 

The basic types may have various modifiers preceding them. The list of modifiers are:

1.     signed

2.     unsigned

3.     short

4.     long

Signed, unsigned, short, lone can be used with int.

Signed, unsigned can be used with char

Long can be used with double.

 

The amount of storage allocated is not fixed. ANSI has the following rules.

 

Short int <= int <= long int

Float <= double <= long double

 

Data types      No. of Bytes               Numeric Range                                Format

1. int                4                                  -2147483648 to 2147483647              %d

2. char             1                                  0 to 255                                               %c

3. float             4                                  -3.4e38 to 3.4e38                                %f

4. double         8                                  -1.7e308          to         1.7e308           %lf or %e

 

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