1. B E GINNING WITH THE
C The Stack
Overflow
Dennis M. Ritchie

2. INTRODUCTION
• C programming language
– Structured and disciplined approach to program design.
 C is developed by Dennis Ritchie
 C is a structured programming language
 C supports functions that enables easy maintainability of code, by breaking
large file into smaller modules
 Comments in C provides easy readability
 C is a powerful language.
 C programs built from
 Variable and type declarations
 Functions
 Statements
 Expressions

3. PROGRAM STRUCTURE
A sample C Program
#include<stdio.h>
int main()
{
--other statements
}

4. HEADER FILES
 The files that are specified in the include section is
called as header file
 These are precompiled files that has some functions
defined in them
 We can call those functions in our program by
supplying parameters
 Header file is given an extension .h
 C Source file is given an extension .c

5. MAIN FUNCTION
 This is the entry point of a program
 When a file is executed, the start point is the main
function
 From main function the flow goes as per the
programmers choice.
 There may or may not be other functions written by
user in a program
 Main function is compulsory for any C program

6. RUNNING A ‘C’ PROGRAM
 Type a program
 Save it
 Compile the program – This will generate an exe file
(executable)
 Run the program (Actually the exe created out of
compilation will run and not the .c file)
 In different compiler we have different option for compiling
and running. We give only the concepts.

7. C LANGUAGE TOKENS
What are actually tokens?
 The smallest individual units in a C program are
known as tokens. In a C source program, the basic
element recognized by the compiler is the "token."
A token is source-program text that the compiler
does not break down into component elements.

8. TOKEN TYPES IN ‘C’
 C has 6 different types of tokens viz.
2.Keywords [e.g. float, int, while]
3.Identifiers [e.g. main, amount]
4.Constants [e.g. -25.6, 100]
5.Strings [e.g. “SMIT”, “year”]
6.Special Symbols [e.g. {, }, [, ] ]
7.Operators [e.g. +, -, *]
C programs are written using these tokens and the general syntax.

9. THE KEYWORDS
 "Keywords" are words that have special meaning to the C compiler.
 Their meaning cannot be changed at any instance.
 Serve as basic building blocks for program statements.
 All keywords are written in only lowercase.

10. KEYWORDS IN ANSI C
auto double register switch
break else return typedef
case enum short union
char etern signed unsigned
const float sizeof void
continue for static volatile
default goto struct while
do if int long

11. THE IDENTIFIERS
 They are programmer-chosen names to represent parts of the program:
variables, functions, etc.
 Cannot use C keywords as identifiers
 Must begin with alpha character or _, followed by alpha, numeric, or _
 Upper- and lower-case characters are important (case-sensitive)
 Must consist of only letters, digits or underscore ( _ ).
 Only first 31 characters are significant.
 Must NOT contain spaces ( ).

12. VALIDITY OF IDENTIFIERS (EXAMPLES)

13. ABOUT CONSTANTS
 Constants in C are the fixed values that do not change during the
execution of a program.
CONSTANTS
Numeric constants Character constants
Real Single
Integer String
Constants Character
Constants Constants
Constants

14. CONSTANTS EXAMPLES
 Integer Constants
 Refers to sequence of digits such as decimal integer, octal integer and
hexadecimal integer.
 Some of the examples are 112, 0551, 56579u, 0X2 etc.
 Real Constants
 The floating point constants such as 0.0083, -0.78, +67.89 etc.
 Single Character Constants
 A single char const contains a single character enclosed within pair of single
quotes [ ‘ ’ ]. For example, ‘8’, ‘a’ , ‘i’ etc.
 String Constants
 A string constant is a sequence of characters enclosed in double quotes [ “ ” ];
For example, “0211”, “Stack Overflow” etc.

15. DECLARATIONS
 Constants and variables must be declared before they can
be used.
 A constant declaration specifies the type, the name and
the value of the constant.
 any attempt to alter the value of a variable defined
as constant results in an error message by the compiler
 A variable declaration specifies the type, the name and
possibly the initial value of the variable.
 When you declare a constant or a variable, the compiler:
1. Reserves a memory location in which to store the value
of the constant or variable.
2. Associates the name of the constant or variable with
the memory location.

16. WHAT ARE VARIABLES IN C?
 A Variable is a data name that is used to store any data value.
 Variables are used to store values that can be changed during the
program execution.
 Variables in C have the same meaning as variables in algebra. That is,
they represent some unknown, or variable, value.
x=a+b
z + 2 = 3(y - 5)
 Remember that variables in algebra are represented by a single
alphabetic character.

17. NAMING VARIABLES
 Variables in C may be given representations containing multiple
characters. But there are rules for these representations.
 Variable names in C
 May only consist of letters, digits, and underscores
 May be as long as you like, but only the first 31 characters are
significant
 May not begin with a number
 May not be a C reserved word (keyword)
 Should start with a letter or an underscore(_)
 Can contain letters, numbers or underscore.
 No other special characters are allowed including space.

18. NAMING CONVENTIONS
 C programmers generally agree on the following conventions for
naming variables.
 Begin variable names with lowercase letters
 Use meaningful identifiers
 Separate “words” within identifiers with underscores or mixed
upper and lower case.
 Examples: surfaceArea surface_Area
surface_area
 Be consistent while naming the variables!
 Use all uppercase for symbolic constants (used in #define
preprocessor directives).
 Examples:
#define PI 3.14159
#define AGE 52

19. CASE SENSITIVITY
 C is a case sensitive language.
 It matters whether an identifier, such as a variable name,
is uppercase or lowercase.
 Example:
area
Area
AREA
ArEa
are all seen as different variables by the compiler.

20. DECLARING VARIABLES
 Before using a variable, you must give the compiler some
information about the variable; i.e., you must declare it.
 The declaration statement includes the data type of the
variable.
 Examples of variable declarations:
int length ;
float area ;

21. DECLARATION (CONTD.)
 Variables are not automatically initialized. For example, after
declaration
int sum;
the value of the variable sum can be anything (garbage).
 Thus, it is good practice to initialize variables when they are declared.
 Once a value has been placed in a variable it stays there until the
program alters it.

22. DATA TYPES IN ‘ANSI C’
 There are three classes of data types here::
 Primitive data types
 int, float, double, char
 Aggregate OR derived data types
 Arrays come under this category
 Arrays can contain collection of int or float or char or double data
 User defined data types
 Structures and enum fall under this category.

23. DATA TYPES- DIFFERENT ATTRIBUTES
Type Size Representation Minimum range Maximum range
char, signed char 8 bits ASCII -128 127
unsigned char bool 8 bits ASCII 0 255
short, signed short 16 bits 2's complement -32768 32767
unsigned short 16 bits Binary 0 65535
int, signed int 16 bits 2's complement -32768 32767
unsigned int 16 bits Binary 0 65535
long, signed long 32 bits 2's complement -2,147,483,648 2,147,483,647
unsigned long 32 bits Binary 0 4,294,967,295
float 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38
double 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38
long double 32 bits IEEE 32-bit 1.175495e-38 3.4028235e+38

24. DATA TYPES : 1- INTEGER
 An integer type is a number without a fractional part.
 Represents a signed integer of typically 4 or 8 bytes (32 or
64 bits).
 Precise size is machine-dependent.
 Designed to hold whole numbers
 Can be signed or unsigned:
 12 -6 +3
 Available in different sizes (number of bytes): short int,
int, and long int
 Size of short int ≤ size of int ≤ size of long int

25. DECLARATION OF INTEGER VARIABLES
 Declarations tell the compiler what variable names will
be used and what type of data each can handle (store).
 Variables of integer type can be defined
- On separate lines:
int length;
int width;
unsigned int area;
- On the same line:
int length, width;
unsigned int area;

26. DATA TYPE: 2- CHARACTER
 Represents a single byte (8 bits) of storage.
 Used to hold characters like ‘d’ or ‘x’ etc..
 Can be signed or unsigned
 Internally char is just a number
 Numerical value is associated with character via a character set.
 ASCII character set used in ANSI C
 Numeric value of character is stored in memory:
MEMORY:
CODE:
letter
char letter;
letter = 'C'; 67

27. DECLARATION OF CHARACTER
VARIABLES
Variables of character type can be
defined:
- On separate lines:
char x;
- On the same line:
char x, y;

28. CHARACTER DATA
 A variable or a constant of char type can hold an ASCII character.
 When initializing a constant or a variable of char type, or when changing
the value of a variable of char type, the value is enclosed in single
quotation marks.
Examples:
const char star = '*';
char letter, one = '1';

29. DATA TYPES: 3- FLOATING-POINT
 A floating-point type is a number with a fractional part
 Represent typically 32 bit real numbers.
 Designed to hold real numbers
12.45 -3.8
 All numbers are signed.
 Available in different sizes (number of bytes): float,
double, and long double
 Size of float ≤ size of double
≤ size of long double

30. DECLARATION OF FLOATING POINT
VARIABLES
 Variables of floating point type can be defined:
- On separate lines:
double x;
float y;
long double z;
- On the same line:
double x, y;
float y , e;
long double z , r;

31. QUICK RESPONSE! 
 Question:
char ch= ‘A’;
 what is the difference between:
1. printf(“%c”, ch);
3. printf(“%d”, ch);

32. Is void a kind of a data type?
Yes or No??

33. DATA TYPE: 6-VOID
The void data type has no values and
no operations.

34. Operators &
Expressions in C
Stack Overflow
2011

35. ABOUT Operators and expressions
• They decide the semantics of expression
• Meaning of operator given in language system.
• Expressions are formed by combining variables with operators and
ALWAYS return a single value in C.
i = 5;
i < j;
a = (a < b);
C supports a rich set of
operators that allow the
programmer to
manipulate variables

36. Operators- Types
• Arithmetic Operators (+, -, *, /, %)
• Relational Operators (<, >, <=, >=, ==, !=)
• Logical Operators (&&, ||, !)
• Bitwise Operators (&, |)
• Assignment Operators (=)
• Increment/Decrement Operators.
• Conditional Operators.
• Special operators.

37. ARITHMETIC OPERATORS
 Used for performing numeric calculations
• Arithmetic calculations
• Use * for multiplication and / for division
• Integer division truncates remainder
• 7 / 5 evaluates to 1
• Modulus operator(%) returns the remainder
• 7 % 5 evaluates to 2
• Operator precedence
• Some arithmetic operators act before others (i.e., multiplication
before addition)
• Use parenthesis when needed
• Example: Find the average of three variables a, b and c
• Do not use: a + b + c / 3
• Use: (a + b + c ) / 3

38. Arithmetic Operators (Contd.)
• Arithmetic Operators::
C operation Arithmetic Algebraic C expression
operator expression
Addition + f+7 f + 7
Subtraction - p–c p - c
Multiplication * bm b * m
Division / x/y x / y
Modulus % r mod s r % s

39. Arithmetic Operators (Contd.)
• RULES OF OPERATOR PRECEDENCE::
Operator(s) Operation(s) Order of evaluation (precedence)
() Parentheses Evaluated first. If the parentheses are nested, the
expression in the innermost pair is evaluated first. If there
are several pairs of parentheses “on the same level” (i.e.,
not nested), they are evaluated left to right.
*, /, or % Multiplication,Divi Evaluated second. If there are several, they are
sion, Modulus evaluated left to right.
+ or - Addition Evaluated last. If there are several, they are
Subtraction evaluated left to right.

40. Arithmetic (summary)
• Five simple binary arithmetic operators
• + “plus”  c = a + b
• - “minus”  c = a - b
• * “times”  c = a * b
• / “divided by” c = a/b
• % “modulus” c = a % b
Q. What are the values of c in each case above if
1. int a = 10, b = 2;
2. float a = 10, b = 2;
3. int a = 10; float b = 2; ??

41. Relational Operators
 Six basic operators for comparison of values in C. These are
typically called relational operators:
1. > “greater than”
2. < “less than”
3. >= “greater than or equal to”
4. <= “less than or equal to”
5. == “is equal to”
6. != “is NOT equal to”
• A relational operator compares two values of C built
in data types such as char, int, float
• Relational operators return Boolean values:
• 0 if relation is FALSE
• 1 if relation is TRUE

42. Relational (contd.)
Standard algebraic C equality or Example of C Meaning of C
equality operator or relational condition condition
relational operator operator (Syntax) Taking 2 variables
‘x’ and ‘y’
Equality Operators
= == x == y x is equal to y
NOT = != x != y x is not equal to y
Relational Operators
> > x > y x is greater than y
< < x < y x is less than y
>= >= x >= y x is greater than or
equal to y
<= <= x <= y x is less than or
equal to y

43. Relational (contd.)
• Example:
int x=44;
int y=12;
(x == y) // false... Returns 0
(x >= y) // true... Returns 1
(x != y) // true ... Returns 1

44. Relational Operator Compliments
• Among the six relational operators, each one is the
compliment of another operator such as,
 > is compliment of <=
 < is compliment of >=
 == is compliment of !=

45. LOGICAL OPERATORS
• Logical Operators are used to create compound expressions
• There are three logical operators in C
1. || “logical OR”
♦ A compound expression formed with || evaluates to 1 (true) if
any one of its components is true
2. && “logical AND”
♦ A compound expression formed with && evaluates to true if
all of its components are true
3. ! “logical NOT” is used to define a compliment of any given
expression or value or variable
Logical operators, like relational operators, are typically used in
conditional expressions
1. if ( (a == 1) && (b < 3) || (c == 1) ) etc.
• However, these can also be used in regular expressions

46. Logical operator- Truth Table
Operand-1 Operand-2 Op1 && Op2 Op1 | | Op2
(Op1) (Op2) (Logical AND) (Logical OR)
Non-zero value Non-zero value 1 1
Non-zero value 0 0 1
0 Non-zero value 0 1
0 0 0 0
Some examples of Logical operators can be::
2.if( age> 55 && salary < 1000)
3.If (number <0 || number >1000)

47. Relative Precedence
• The relative precedence of the relational as well as
logical operators is as follows::
• HIGHEST !
> >= < <=
== !=
&&
• LOWEST ||

48. ASSIGNMENT OPERATORS
• The operator symbol is the equal sign ( = )
• The expression on the right-hand side is evaluated and assigned to
the left-hand variable.
int x = 9;
• Assignment operators are used to assign the result of an expression
to a variable. C provides the facility of shorthand assignment
operators of the form::
variable op= expression
• Some examples are::
x= x+y can be written as x+=y
a=a*(n+1) can be written as a *= n+1
z= z%d can be written as z%=d

49. INCREMENT/DECREMENT OPERATORS
• In C, we have 2 very useful operators called the
increment & decrement operators:
• Increment : ++ adds 1 to the operand
• Decrement : -- subtracts 1 from the operand
• Both the operators are unary and take the following
form::
++x; OR x++;
--y; OR y--;

50. Rules for ++ and – – operators
• ++ and – – are unary operators; they require variable as their
operands.
• When postfix ++ (or – –) is used with a variable in an exp., the
expression is evaluated first using the original value of the
variable and then the variable’s value is accordingly
incremented or decremented.
• When prefix ++ (or – –) is used with a variable in an exp.,
firstly, the variable’s value is accordingly incremented or
decremented and then the expression is evaluated using the
new value of the variable.
• The precedence and associativity if ++ & – – are same as that
of unary + and unary –.

51. CONDITIONAL OPERATORS
• The operators ? and : are called conditional operators as
they are used to test the conditions in the conditional
expressions.
• Conditional expression ::
• Format: <Expression 1> ? <Expression 2> : <Expression 3>
• Example:
x ? y : z
Test Condition True expression False expression

52. Use of Conditional Operators
 Now consider these
Consider the
statements:
following statements:
a=80;
a= 80; b=95;
b= 95; z= (a>b) ? a : b;
if(a>b)
z=a;
else Both the statements are
resulting the same values.
z=b; This is an example of
usage of conditional
expressions

53. BITWISE OPERATORS
• Perform bitwise logical operations across individual bits of a value.
• AND &
• OR | x : 1 0 1 0 (binary)
• XOR (exclusive OR) ^ y : 1 1 0 0 (binary)
• NOT ~ x & y : 1 0 0 0 (binary)
(1’s complement)
x | y : 1 1 1 0 (binary)
• Shifts are bitwise operators x ^ y : 0 1 1 0 (binary)
• SHIFT LEFT << ~x : 0 1 0 1 (binary)
• SHIFT RIGHT >>
x << y shift x y-places to the left (add zeros)
x >> y shift x y-places to the right (sign extend)

54. THE COMMA ( , ) OPERATOR
• This operator is used to link the related expressions together
• A comma-linked expression is evaluated from left to right &
the value of the right most expression is the value of combined
expression. Say,
val = ( x=10, y=5, x+y)
x is firstly assigned the value as 10, then y is assigned as 5 and then 15
(10+5) is being assigned to the val
• This operator is used in for loops, while loops etc.
• FOR loop
for(i=0, j=1; i<=10 ; i++, j++);
• WHILE loop
while(c =getchar(), c!= ‘20’)
• Interchanging values
z=a, a=b, b=z;

55. THE SIZEOF OPERATOR
• The sizeof operator is used with an operand to return the
number of bytes the operand occupies. The operand may be a
variable, a constant or a data type qualifier.
• It’s a compile time operator.
• Mainly used to find the length of arrays and structs when their
sizes are unknown.
• Also used to allocate memory spaces dynamically to different
variables while any program execution.
• For example::
k= sizeof (sum);
j= sizeof(long int);
w= sizeof(32767);

56. Rules of Precedence & Associativity
• Precedence rule decides the order in
which different operators are
applied.
• Associativity rule decides the order in
which multiple occurrences of the
same operator are applied.

57. OPERATOR PRECEDENCE/ASSOCIATIVITY
OPERATORS (precedence from HIGHER to LOWER) ASSOCIATIVITY
( ) [ ] -> . left to right
! ~ ++ -- + - * & (type) sizeof right to left
* / % left to right
+ - left to right
<< >> Bitwise left to right
< <= > >= Relational left to right
== != Relational left to right
& Bitwise left to right
^ Bitwise left to right
| Bitwise left to right
&& Logical left to right
|| Logical left to right
?: right to left
= += -= *= /= %= &= ^= |= <<= >>= right to left
, left to right