# Constants

Constants in C refer to fixed values that do not change during the execution of a program. C supports several types of constants as shown in previous tutorials.

### Integer Constants

Refers to the order of the constant digits of an integer. There are three types of decimal integers, octal integers, and hexadecimal integers. Decimal integers consist of a set of digits, 0 through 9, preceded by an optional - or + sign. An effective example of a decimal integer constant is:

123   -321   0   654321   +78

The constant of an octal integer sets any number from 0 to 7 with a top 0.

A sequence of digits before 0x or 0X is considered a hexadecimal integer. They can include the alphabet A through F or complete f. The letter through F represents a number from 10 to 15.

### Sample Program

###### Program
```#include <stdio.h>
int main()
{
printf("Integer values are \n");
printf("%d %d",1000,1000+10);
return 0;
}
```

### Real Constants

The number of integers is insufficient to represent a continuous quantity, such as distance, height, temperature, price, etc. These quantities are represented by fractional numbers such as 18.532. These national numbers are called real constants. Another example of a real constant is:

0.0032   -9.312   231.98   +21.90

These numbers appear in decimal notation after a whole number of decimal points and fractions. Digits before the decimal point or digits after the decimal point can be omitted.

219.   .45   -.12   +.9

### Examples of Numeric Constants

Constant Valid? Remarks
789798L Yes Represents long integer
10,000 No Comma is not allowed
+3.6E2 Yes (ANSI C supports unary plus)
3.6E-2 Yes
3.6e 3 No white space not allowed
1.7E+3.5 No Exponent must be an integer
\$288 No \$ symbol is not permitted

### Single Character Constants

A single character constant consists of a single character bound in a pair of constant single quotation marks. Examples of character constants are:

'9'   'K'   ';'   ' '

Note that the character constant '9' is not the same as the number 9. The last constant is a blank space.

The character contains integer values known as ASCII values. For example,

```printf("%d",'b');
// output 98
```

```printf("%c",'b');
// output b
```

### String Constants

A string constant is a double-quote sequence of characters. Characters can be letters, numbers, special characters, and spaces. Examples are:

"World"   "2000"   "Hello World"   "A"

Note that a character constant (e.g., 'a') is not equivalent to a single-character string constant (e.g., "A"). Furthermore, a single-character string constant does not have an integer value equivalent, but a character constant has an integer value. Character strings are often used in programs to create meaningful programs.

### Backslash Character Constants

C supports some special backslash character constants that are used in output methods. For example, the symbol '\b' stands for backspace. All backslash character constants are given in the table below:

Constant Meaning