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• Constant in C language are also the name given to the data values stored in memory like variable but the value of constant cannot be changed at the time of execution.
• There are several types of Constants in C. They are classified in the two groups as given below in the figure: #### Numeric Constants

Numeric constants can be of two types Integer and real constants:

##### Integer Constants
• Integer constant are sequence of number from digits 0 to 9 without any decimal point or fractional parts.
• Integer constants can be positive or negative.
• The number without any sign assumed to be positive number.
• Integer constants can be of minimum 2 bytes and maximum 4 bytes.
• Here are some examples of Integer constants:
45, -16, +56, 67 etc.
##### Real Constants
• Real constant are also known as floating point constants which contains decimal point as well as fractional parts.
• Real constants can be positive or negative.
• The number without any sign assumed to be positive number.
• Real constants can be written in exponential notation which contains two parts mantissa and exponent.
• The mantissa and exponent part are separated by a letter e.
• Mantissa is a real number represented in decimal or integer it can be positive or negative. Whereas exponent is an integer number that can be positive or negative.
• Here are some examples of real constants:
+2.7, -3.8, 6.7, 4.5 etc

+1.5e+6

-3.8e6

3.4e-7 etc.

#### Character Constants

Character constants can be categorized into two parts:

##### Single Character Constants
• A single character constant can be a alphabet, digit or special symbol enclosed in single quote.
• Single character requires only one byte.
• Here are some examples of single character constants:
‘A’, ‘b’, ‘@’, ‘8’ etc.
##### String Constants
• String constants in c are sequence of characters enclosed in double quotes.
• Here are some examples of string constants:
“Ram”, “Good”,”1234″, “@@@@”

### Declaration of Constants

• You have to declare the constant before using it into the program.
• Constant is declared using the keyword ‘const’.
• Here is the syntax for declaring constant in C.
const data-type constant_name=data_value;
• Some examples of declaring constant in C++ are given here:
const int a=10;

const float b=10.34;

const char c=’a’;

• Here is an example of using constant in C program:
``` #include<iostream.h> int main() { const int a=10;/*constant declaration*/ printf("nvalue of a is:%d",a); return 0; } ```

• The output of the above program is as follows:
value of a is:10 