 Constants 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 constant are present 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
3.4e7 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 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 datatype 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