Constants in C Programming Language

Constant is a quantity in C whose value does not change ever. This quantity stored in memory at any certain location of Computer. There are mostly two type of constant which are given below.

1. Primary Constant
2. Secondary Constant

These constant are further categorized as shown in figure

But at this stage our focus will we on Primary Constants, namely  Numeric and Character Constants.

Rules For Constructing Integers Constants

An integer constant means a sequence of digit. There are three type of Integer constant which are decimal integers, octal integer and hexadecimal integer.  

Decimal integers contain digit from 0 to 9 with optional sign – or + which indicate that number is positive or negative.  Valid set of decimal integers are 

+ 123, 123, 456, -34, -542, 0, 76543

While space, commas, and non-digit characters are not entertained between digits. For example –

15-234, 23,000, 43 434, $3454

are illegal numbers.

1. An integer constant must at least one digit.
2. Decimal point must not be allowed
3. Number could be positive or negative.
4. If no sign used before number, it means integer Constant assumed to be positive.
5. No comma, blank space, and dollar sign must within or before an integer constant.

Integer Constant have range limitation which vary according machine. If you working 16 bit computer , integer constant range will vary between -32768 to +32767

Rules For Constructing Real Constants

Integer constant are unable to calculate measurement problem and cost estimated problem because these quantities are represented  by number containing fraction part like 13.456. this numbers are called real number or floating points number

For example –

23.54554, -544534.56546, +45345.5534

Floating points number or real Constant are those number that contain decimal points between digits but remember point will be between digit not before neither after like .43 or 4343.

Valid	Invalid
443.4434, -434.546, +55.54	.4545, -.5345, 45354. , -53454.

1.  A real number must be at least  two digit with one decimal point.
2. It could be either positive or negative.
3. Default sign assumed positive.
4. No comma, blank space are allowed between number except decimal point.

There are another way to represent real number is exponential notation or scientific notation. In this type of notation two part exist that joined with e character. Like 32.334e2

First part of this notation is called mantissa and second part of this notation called exponent. This method of real number we will descius in last chapter.

Rules For Constructing Character Constants

Character constant is a single character from character set of C that enclosed by single quote marks. Examples of character constant are

‘5’           ‘a’           ‘;’            ‘ ’

Maximum length of character constant must be 1 with enclosed by single quote.

Above ‘5’ is character constant and it is not equal to 5 because 5 is digit and ‘5’ is character constant.  Every character constants have integer value known as ASCII values. ‘5’ integer value is 53 and integer value of ‘a’ is 97.

There are many discussion are remaining on this section we will later in Next related Section

Rules for Constructing String Constant

A string constant is sequence of character that enclosed by double quotes. This character may be numbers, alphabets and special symbols and also blank space. Example are

“How are you”                  “1988”                   “WELL DONE”                    “? $%^%$#”                       “3+4=7”

There you should mind that character constant is not equivalent to string constant example (“x” is not equivalent to ‘x’)

1. String Constant should be enclosed with double quotes.
2. String Constant contains all digit, special symbols and alphabets.
3. String constant contain blank space.

Backslash Character Constants

There is special character constants that used with output function in C. every Backslash character constant used with specific reason during outputting. For example, the symbol ‘\n’ stands here for newline character that tells signal to computer print new line after this ‘\n’ new line symbol.