9.13.2011

C Programming Fundamentals:Constants

The Constants in C are those identifiers which value are never change.There are four basic types of constants in C:

1. integer constants

2. floating-point constants

3. character constants

4. string constants


 3 different number systems are used:

decimal, octal and hexadecimal.

Some valid decimal integer constants:

0     1       743        5280   32767     9999

Some invalid decimal integer constants:

12,245      36.0      10 20 30    123-45-678   0900


Some valid octal integer constants:

0        01           0743           077777

Some invalid octal integer constants:

743           05280              0777.777

Some valid hexadecimal integer constants:

0X1      0X7FFF      0xabcd

Some invalid hexadecimal integer constants:

0X12.34       0BE38       0x.4bff      0XDEFG


Unsigned and long integer constants


50000U(decimal unsigned)
123456789L(decimal long)
123456789UL(decimal unsigned long)
0123456L(octal long)
0777777U(octal unsigned)
0X50000U(hexadecimal unsigned)
0XFFFFFUL(hexadecimal unsigned long)

Floating-Point Constants

A floating-point number is a base-10 number that contains either a decimal point or an
exponent(or both). Some valid floating-point constants:

0.          1.             0.2                 827.602
5000.                 0.000743                       12.3                315.0066
2E-8                   0.006e-3                  1.6667E+8          .12121212e12


Some illegal floating-point constants:

1

1,000.0

2E+10.2

2E 10


Character Constants

A character constant is a single character enclosed in apostrophes(i.e., single quotation
marks)

Example: ‘A’          ‘x’              ‘3’               ‘?’              ‘ ’
                  65         120              51               63             32


String Constants

A string constant consists of any number of consecutive characters(including none),
enclosed in double quotation marks.

Examples:

“green”         “Oxford University, UK”
“270-32-3456”             “$19.95”             “ ”
“Line 1\nLine 2\nLine3”               “\tTo be continued”

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