**Constants** are similar to the variables except that their value **remains fixed**. Therefore constants are those values which **remains unchanged or unaltered** throughout the program execution. Constants are also called as **literals**. They can be of any basic data types.

## Defining a Constant

There are two way by which we can define a constant:

- using the
**#define**preprocesser - using the
**const**keyword

### 1. Using the **#define** preprocesser

##### Syntax for defining constant using #define preprocesser

```
#define identifier value;
```

### Program example using #define preprocesser directive

```
#include<stdio.h>
#define PI 3.14
int main()
{
int radius = 5;
float area;
area = PI*radius*radius;
printf("Area of circle with radius %d is %f\n", radius, area);
return 0;
}
```

### Output

```
Area of circle with radius 5 is 78.500000
```

### 2. Using the **const** keyword

##### Syntax for defining a constant using const keyword

```
const type var_name = value;
```

### Program example using const keyword

```
#include<stdio.h>
int main()
{
const float PI = 3.14;
int radius = 5;
float area;
area = PI*radius*radius;
printf("Area of circle with radius %d is %f\n", radius, area);
return 0;
}
```

### Output

```
Area of circle with radius 5 is 78.500000
```

## Types of Constants

**Integer constants**Integer constans are the integer numeric values without fraction.

**Example**: 1, 2, 0xFFF, etc. There are different types of integer constans like:- Decimal constant
- Hexa-decimal constant
- octal constant

**Floating-point constants**Floating-point constants are the numeric constants having decimal points or have fractional parts.

**Example**: 1.245, 2.55, etc.**Character constants**Character constants are those that are enclosed inside the single quotes. The character constants have the

**char**data type.**Example**: ‘A’, ‘S’, etc.**String Literals**String literals are those constants that are enclosed inside the double quotes. They are the sequence of characters. String literals also have the

**char**data type.**Example**: “OjhaBikash”, “Hello world”, “Constants”, etc.