Elements of C (Lesson)

Elements of C Programming

To write programs in C, we need to understand the fundamental building blocks, often referred to as tokens.

4.1 Character Set

The character set in C includes:

Alphabets: A-Z, a-z
Digits: 0-9
Special Characters: + - * / % ^ & ( ) [ ] { } = < > . , : ; ' " ! # _
White Spaces: Space, Tab, Newline, Form-feed.

4.2 C Tokens

The smallest individual units in a C program are called Tokens.

Keywords
Identifiers
Constants
Strings
Special Symbols
Operators

4.3 Keywords and Identifiers

Keywords

Keywords are reserved words whose meaning is already known to the compiler. There are 32 keywords in C: auto, break, case, char, const, continue, default, do, double, else, enum, extern, float, for, goto, if, int, long, register, return, short, signed, sizeof, static, struct, switch, typedef, union, unsigned, void, volatile, while.

Identifiers

Identifiers are names given to variables, functions, and arrays. Rules for naming identifiers:

Must begin with a letter or underscore (_).
Can contain letters, digits, and underscores.
No special characters allowed (except _).
Keywords cannot be used as identifiers.
C is case-sensitive (Age and age are different).

4.4 Data Types in C

Data types specify what kind of data a variable can store.

Type	Description	Size (typical)	Format Specifier
`int`	Integers (whole numbers)	4 bytes	`%d`
`char`	Single character	1 byte	`%c`
`float`	Simple floating point (decimals)	4 bytes	`%f`
`double`	Double precision floating point	8 bytes	`%lf`
`void`	Represents "empty" or "no type"	-	-

4.5 Variables and Constants

Variables

A variable is a container (memory location) whose value can change during program execution.

int score = 100; // Initialization
score = 200; // Re-assignment

Constants (Literals)

Constants are fixed values that do not change. Ways to define constants in C:

Using const keyword:
```
const float PI = 3.14159;
```
Using #define preprocessor:
```
#define MAX_BUFFER 1024
```

4.6 Escape Sequences

Special character sequences used to represent certain whitespace or control characters.

\n: Newline
\t: Horizontal tab
\\: Backslash
\': Single quote
\": Double quote
\0: NULL character

See the Lecture Slides for a full table of Data Type ranges and modifiers (short, long, signed, unsigned).