The C Character Set : Constants, Variables and Keywords

A character denotes any alphabet, digit or special symbol used to represent information. Here is the list of valid character set (Alphabets, Numbers and Symbols) allowed in C.

The alphabets, numbers and special symbols when properly combined form constants, variables and keywords. Let us see what are ‘constants’ and ‘variables’ in C.

Constant and Variable in C:

• A constant is an entity that doesn’t change
• A variable is an entity that may change.

In any program we typically do lots of calculations. The results of these calculations are stored in computers memory. Like human memory the computer memory also consists of millions of cells. The calculated values are stored in these memory cells. To make the retrieval and usage of these values easy these memory cells (also called memory locations) are given names. Since the value stored in each location may change the names given to these locations are called variable names.

Let’s have an example:

1. Here 3 is stored in a memory location and a name x is given to it.
2. Then we are assigning a new value 5 to the same memory location x.
3. This would overwrite the earlier value 3, since a memory location can hold only one value at a time.
4. Since the location whose name is x can hold different values at different times x is known as a variable.
5. As against this, 3 or 5 do not change, hence are known as constants.

C Keywords:

• Keywords are the words whose meaning has already been explained to the C compiler (or in a broad sense to the computer).
• The keywords cannot be used as variable names because if we do so we are trying to assign a new meaning to the keyword, which is not allowed by the computer.
• Some C compilers allow you to construct variable names that exactly resemble the keywords.However, it would be safer not to mix up the variable names and the keywords.
• The keywords are also called ‘Reserved words’.
• There are only 32 keywords available in C.
• Below are the list of keywords used in C.

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