# Learn C Language

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# Constant In C

Constant is an entity that doesn’t change. You know very well that any software is developed to handle some information. This information nothing but a constant that never changes. Sometimes, it is also called as data.

In other words, a fixed value that may not be altered by a program during its execution is called constant. **A constant in c programming is also called as literal. **Moreover, you can assume a constant as a regular variable whose value can not be modified after its definition. Any basic data type like a floating constant, an integer constant, a character constant or a string literal can be a constant in c programming. By the way, in the C language **enumeration** constant also exist.

## Types Of Constant

Constants can be categorized as Primary constant and secondary constant.

- Primary Constant
- Secondary Constant

## Primary Constant

Fundamental constants or basic constants are called as primary constants. There are three types of primary constant.

- Character Constant
- Integer Constant
- Real Constant

## Character Constant

All character symbols are character constants if they are enclosed in a single quote and of unit length.

## Rules To Construct Character Constant

- A character constant is a single alphabet, a single digit or a single special symbol enclosed within a single quote or inverted commas ‘ ‘.
- In addition, both inverted commas should point to left.

**Let’s see a few examples of Character Constant:**

**Integer Constant**

All numbers either positive or negative without the decimal point are an integer constant. It can be a decimal, octal, or hexadecimal constant. An integer constant in c programming might have a prefix that specifies the base or radix : 0 for octal, 0x or 0X for hexadecimal.

An integer constant in c programming can also have a suffix that is a combination of U (unsigned ) and L (long). The suffix of an integer constant can be uppercase or lowercase and can be in any order.

## Rules To Construct Integer Constant

- An integer constant must have at least one digit.
- It must not have a decimal point.
- An integer constant can be either positive or negative.
- If no sign precedes then integer constant is assumed to be positive.
- No blank space or commas are allowed within an integer constant.
- Mostly the allowable range for integer constant is -2147483648 to +214748647. However, the range of an integer constant depends upon the compiler. For compilers like visual studio, gcc, the range mentioned above is true whereas for compilers like turbo the range is -32768 to +32767.

**Let’s see a few examples of Integer Constant:**

**Real Constant**

All numbers either positive or negative wit the decimal point involved is a real constant.

Real constants are often called Floating-point constants. The real constants could be written in two forms Fractional form and Exponential Form. The exponential form is usually used if the value of the constant is either too small or too large. In addition, a floating-point constant has an integer part, a decimal point, a fractional part, and an exponent part.

## Rules To Construct Real Constant

- A real constant must have at least one digit.
- It must have a decimal point.
- Likewise an integer constant, real constant could be positive or negative.
- Of course, the default sign is positive.
- Similar to an integer constant, in real constant also commas or blanks are not allowed.

**Let’s see a few examples of Real Constant:**

## Rules To Construct Real Constant (Type2)

Following rules must be especially observed while constructing real constant in c programming that is expressed in **exponential form.**

- The mantissa part may have a positive or negative sign.
- Moreover, the default sign of mantissa is positive.
- Furthermore, the mantissa part and the exponential part should be separated by
**e or E.** - The exponent must have at least one digit, which may be positive or negative. However, the default sign is positive.

**Let’s see a few examples of Real Constant (Type2):**

**Secondary Constant**

Secondary constants are also known as **a derived constant** in c programming. Because they are derived from primary constants.

**Arrays, strings, pointers, structures, union, enumerators are secondary constants.** Please, read about these in upcoming tutorials as these are very important and big topics. So, I have covered these topics separately.

## How to Define Constants?

You can define constants in two ways :

- Using
**#define****preprocessor.** - The other is using,
**const****keyword.**

## Using Preprocessor :

## Using const Keyword :

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