To store data inside the computer we need to first identify the type of data elements we need in our program. There are several different types of data, which may be represented differently within the computer memory. The data type specifies two things:
- Permissible range of values that it can store.
- Memory requirement to store a data type.
C language provides 4 basic data types viz., int, char, float and double. Using these, we can store data in simple ways as single elements or we can group them together and use different ways to store them as per requirement. The 4 basic data types are described in below table.
| Data Type | Type of Data | Memory | Range |
|---|---|---|---|
| char | char | 8 | -127 to 128 |
| unsigned char | char | 8 | 0 to 255 |
| signed char | char | 8 | -127 to 128 |
| int | int | 16 or 32 | -32767 to 32768 |
| unsigned int | int | 16 or 32 | 0 to 65,535 |
| signed int | int | 16 or 32 | same as int |
| short int | int | 16 | -32767 to 32768 |
| unsigned short int | int | 16 | 0 to 65,535 |
| signed short int | int | 16 | same as short int |
| long int | int | 32 | -2,147,483,647 to 2,147,483,647 |
| long long int | int | 64 | -(2*63-1) to 2*63 -1 (Added by C99) |
| signed long int | int | 32 | same as long int |
| unsigned long int | int | 32 | 0 to 4,294,967,295 |
| unsigned long long int | int | 64 | 2*64 -1 (Added by C99) |
| float | float | 32 | 1E-37 to 1E+37 with six digits of precision |
| double | double | 64 | 1E-37 to 1E+37 with six digits of precision |
| long double | double | 80 | 1E-37 to 1E+37 with six digits of precision |
Identifiers
Identifiers are the names given to various program elements such as constant, variable, function names and arrays etc. Every element in the program has its own distinct name but one cannot select any name unless it conforms to valid name in C language. Let us study first the rules to define names or identifiers.
Rules for forming Identifiers
- Identifiers are defined according to the following rules:
- It consists of letters and digits.
- The first character must be an alphabet or underscore.
- Both upper and lower cases are allowed. Some text of different case is not equivalent, for Example: TEXT is not the same as text.
- Except for the special character underscore(_), no other special symbols can be used.
For example, some valid identifiers are as
X
X123
_X123
temp
tax_rate
Keywords
Keywords are reserved words which have a standard, predefined meaning in C. They cannot be used as program-defined identifiers.
The lists of C keywords are as follows:
| char | int | printf | long |
| union | continue | goto | while |
| if | double | enum | const |
| for | sizeof | do | else |
| struct | register | float | signed |
| volatile | typedef | switch | break |
| static | auto | case | return |
| unsigned | default | void | short |
Note: Generally all keywords are in lower case although uppercase of same names can be used as identifiers.
Control characters (Escape sequences)
Certain non printing characters as well as the backslash () and the apostrophe(‘), can be expressed in terms of escape sequence.
- \a – Bell
- \n – New line
- \r – Carriage return
- \b – Backspace
- \f – Formfeed
- \t – Horizontal tab
- \” – Quotation mark
- \v – Vertical tab
- \’ – Apostrophe
- \\ – Backslash
- \? – Question mark
- \0 – Null
