Variables and Keywords

Character Set

Identifiers

Variables & Naming Rules

A Variable is a name given to a memory location where data can be stored and manipulated during program execution.

• The first character must be an alphabet (letter) or an underscore.
• Keywords are reserved and cannot be used as variable names.
• White spaces and blanks are not allowed in variable names.
• C is case-sensitive (UPPERCASE and lowercase letters are treated distinctly).
• Only the underscore (_) special symbol is permitted between characters.
• The identifier length may be up to 31 characters (traditionally the first 8 characters were significant to early compilers).

Local Variables

Local variables are declared within the body of a function and can only be accessed within that function block:

void main() {
    int a, b, c;  // Local to main()
}

void func() {
    int x, y, z;  // Local to func()
}

Global Variables

A global variable is declared outside of any program function, usually at the beginning of the program file after preprocessor directives:

int a, b, c;  // Global variables

void main() {
    // Can access a, b, c
}

void func1() {
    // Can also access a, b, c
}

Keywords in C

Keywords are system-defined reserved identifiers with fixed meanings that cannot be altered or used as variable names.

Escape Sequence Characters (Backslash Constants)

C supports escape sequences used to perform formatting and special tasks, also known as 'Backslash characters':