The document outlines key concepts in C programming including data types, tokens, keywords, identifiers, constants, variables, and scopes. It discusses the five fundamental data types in C (integer, floating-point, double, character, void), tokens like keywords and identifiers, common keywords and their meanings, rules for identifiers, how variables are declared and initialized, what constants are (fixed values that don't change), and the four scopes in C.

1. Lecture02(Constants, variable & data types)
June 15, 2010
Today's Outline
Data Types
C Tokens
Keywords & Identifiers
Constants
Variables
The four C scopes
Type Qualifiers
Storage Class Specifiers
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2. C Tokens
Token: Smallest individual units in C program are known as token.
e.g. Keywords - int, break, for, struct etc
Identifiers - count, amount etc
Constants - 10, 5.5, -7.5 etc
Strings - “DUET”, “1st Year” etc
Operators - +, -, *, /
Special Symbols - [] {} etc
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3. C Data Types
All C compiler supports 5 foundational data types, namely
integer(int), floating-point(float), double precision floating-point
(double), character(char), & void.
Data Type Size (bits)
char 8
int 16 or 32
float 32
double 64
void type either explicitly declares a function as returning no value
or creates generic pointers.
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4. C Keywords
All keywords have fixed meanings & these meanings can not be
changed. Serve as basic building blocks for program statements.
All keyword must be written in lowercase letters.
• Flow control (6) - if, else, return, switch, case,
default
• Loops (5) - for, do, while, break, continue
• Common types (5) - int, float, double, char, void
• Structures (3) - struct, typedef, union
• Counting and sizing things (2) - enum, sizeof
• Rare but still useful types (7) - extern, signed,unsigned,
long, short, static, const
• Evil keywords which we avoid (1) - goto
• Others (3) - auto, register, volatile
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5. C Identifiers
In C, the names of variables, functions, labels & various other user-
defined items are called identifiers.
Rules for identifiers:
• First character must be an alphabet or underscore and subsequent characters
must be either letter, digits, or underscore.
• Only 31 characters are significant.
• Can not be the same as a C keywords & should not have the same name as
functions that are in C library.
• Must not contain white space.
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6. Variables
A variable is a named location in memory that is used to hold a value
that can be modified by the program.
All variable must be declared before they can be used.
Format: type varable_name; e.g. int count;
Variable name must be meaningful to reflect its function or nature.
Variable initializations Format: type variable_name = constant;
Where variables to be declared:
- Inside function (local variables)
- In the definition of function parameters (Formal parameters)
- Outside of all functions (global variables)
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7. Constants
Constants refers to fixed values that do not change during program
execution.
Constants can be of any type of the basic types.
Constants are also called literals.
int 10, 135, -23
Example:
long int 5678349L
unisigned int 580U
unisigned long int 9845464UL
float 120.25f
long double 1020.75L
character constants ‘D’
string “DUET”
HEX 0x80
Octal 016
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8. Backslash Character Constants
Backslash character constants are used in output functions.
Also known as escape sequence
Code Meaning
b Backspace
n New line
f Form feed
r Carriage return
t Horizontal tab
v Vertical tab
” Double quote
’ Single quote
Backslash
a Alert
? Question mark
0 Null
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9. Any Question?
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10. Thank You All
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