Basic Concepts of C programming

1. PROGRAMMING FOR
PROBLEM SOLVING IN C
UNIT – I
Algorithms, building blocks of algorithms
(Statements, State, Control flow, Functions),
notation (Pseudo code, Flow Chart, Programming
language), algorithmic problem solving, simple
strategies for developing algorithms (iteration,
recursion). Introduction to C Programming – Data
types - Operators and Expressions – Data Input
and Output – Decision making and Looping
Statements.
Prepared By,
S.SRIDEVI, CSE

2. Introduction to C
 Ken Thompson at Bell Labs, USA,
wrote his own variant over Martin
Richards’s Basic Combined
Programming Language and called it
B .
 Dennis Ritchie, at Bell Labs, is
credited for designing C in the early
1970s.

3. Why learn C?
a. C is quick.
b. C is a core language : In computing,
C is a general purpose, cross-
platform, block structured procedural,
imperative computer programming
language.
c. C is a small language: C has only
thirty-two keywords. This makes it
relatively easy to learn compared to
bulkier languages.
d. C is portable

4. Steps in executing a C
program

5. Structure of a C program

6. Standard Header Files

7. Variable
 A variable is an identifier for a memory
location in which data can be stored
and subsequently recalled.
 Variables are used for holding data
values so that they can utilized in
various computations in a program.
 data_type variable_name = value;

8. Datatypes

9. Basic Data types – Size and
Range
16 bit computer:
32 bit computer:

10. Specifiers or Modifiers
 In addition, C has four type specifiers or modifiers and
three type qualifiers.
Each of these type modifiers can be applied
to the base type int.
The modifiers signed and unsigned can also
be applied to the base type char.
In addition, long can be applied to double.
When the base type is omitted from a
declaration, int is assumed.
The type void does not have these
modifiers.

11. Specifiers: Data Types
 The specifiers and qualifiers for the data types can be broadly
classified into three types:
Size specifiers— short and long
Sign specifiers— signed and unsigned
 Type qualifiers— const, volatile and restrict

12. Program Statements
 A statement is a syntactic constructions that
performs an action when a program is
executed. All C program statements are
terminated with a semi-colon (;).

13. Program Statements
 Declaration :It is a program statement that serves
to communicate to the language translator
information about the name and type of the data
objects needed during program execution.
 Expression statement: It is the simplest kind of
statement which is no more than an expression
followed by a semicolon. An expression is a
sequence of operators and operands that specifies
computation of a value . Example :x = 4
 Compound statement is a sequence of
statements that may be treated as a single
statement in the construction of larger statements.
 Labelled statements can be used to mark any
statement so that control may be transferred to
the statement by switch statement.

14. Program Statements
 Control statement is a statement whose execution
results in a choice being made as to which of two or
more paths should be followed. In other words, the
control statements determine the ‘flow of control’ in a
program.
Selection statements allow a program to select a
particular execution path from a set of one or more
alternatives. Various forms of the if..else statement
belong to this category.
Iteration statements are used to execute a group
of one or more statements repeatedly. “while, for,
and do..while” statements falls under this group.
Jump statements cause an unconditional jump to
some other place in the program. Goto statement

15. Tokens
 The basic lexical building blocks of source
code.
 Five classes of tokens
 Identifier
 Keywords
 Operators
 Separators
 Constant

16. Identifiers
 An identifier or name is a sequence of
characters created by the programmer to
identify a name or specific object.
 In C, variables, arrays, functions and labels are
named.
 Rules:
First character – alphabet or underscore
_
All characters – alphabets, digits or _
First 31 characters are significant
An identifier cannot duplicate a

17. Keywords
 Keywords form the vocabulary of C.
 They have predefined uses and cannot be
used for any other purpose in a C program.
 They are always written in lowercase letters.
auto double int struct
break else long switch
case enum register typedef
char extern return union
const float short unsigned
continue for signed void
default goto sizeof volatile
do if static while

18. Constants
 A constant is an explicit data value written by the
programmer. Thus, it is a value known to the compiler
at compiling time.

19. Operators in C

20. Different Operators

21. Arithmetic Operators
 There are three types of arithmetic operators in C:
binary, unary, and ternary.
 Binary operators: C provides five basic arithmetic
binary operators.
 Arithmetic binary operators:

22.  Unary operators: The unary ‘–’ operator negates the
value of its operand (clearly, a signed number). A numeric
constant is assumed positive unless it is preceded by the
negative operator. That is, there is no unary ‘+’. It is
implicit. Remember that -x does not change the value of x
at the location where it permanently resides in memory.
 Unary increment and decrement operators ‘++’ and ‘--’
operators increment or decrement the value in a variable
by 1.
 Basic rules for using ++ and – – operators:
The operand must be a variable but not a constant or an
expression.
 The operator ++ and -- may precede or succeed the
operand.
Unary Operators

23. Postfix:
 (a) x = a++;
First action: store value of a in memory location for variable x.
Second action: increment value of a by 1 and store result in
memory location for variable a.
 (b) y = b– –;
 First action: put value of b in memory location for variable y.
 Second action: decrement value of b by 1 and put result in
memory location for variable b.
Postfix

24. Prefix :
• (a) x = ++a;
First action: increment value of a by 1 and store result in
memory location for variable a.
Second action: store value of a in memory location for
variable x.
• (b) y = – –b;
First action: decrement value of b by 1 and put result in
memory location for variable b.
Second action: put value of b in memory location for
variable y.
Prefix

25.  C provides six relational operators for comparing
numeric quantities. Relational operators evaluate to 1,
representing the true outcome, or 0, representing the
false outcome.
Relational Operators

26.  C provides three logical operators for forming logical
expressions. Like the relational operators, logical
operators evaluate to 1 or 0.
Logical negation is a unary operator that negates the
logical value of its single operand. If its operand is non-
zero, it produces 0, and if it is 0, it produces 1.
Logical AND produces 0 if one or both its operands
evaluate to 0. Otherwise, it produces 1.
Logical OR produces 0 if both its operands evaluate to
0. Otherwise , it produces 1.
Logical Operators

27.  C provides six bitwise operators for manipulating the
individual bits in an integer quantity . Bitwise operators
expect their operands to be integer quantities and treat
them as bit sequences.
Bitwise negation is a unary operator that complements
the bits in its operands.
Bitwise AND compares the corresponding bits of its
operands and produces a 1 when both bits are 1, and 0
otherwise.
 Bitwise OR compares the corresponding bits of its
operands and produces a 0 when both bits are 0, and 1
otherwise.
Bitwise exclusive or compares the corresponding bits of
its operands and produces a 0 when both bits are 1 or
both bits are 0, and 1 otherwise.
Bitwise Operators

28. Bitwise Operators

29.  The conditional operator has three expressions.
 It has the general form expression1 ?
expression2 : expression3
First, expression1 is evaluated; it is treated as a
logical condition.
If the result is non-zero, then expression2 is
evaluated and its value is the final result.
Otherwise, expression3 is evaluated and its value
is the final result.
 For example,int m = 1, n = 2, min;
min = (m < n ? m : n); /* min is assigned a value 1 */
 In the above example, because m is less than n,
m<n expression evaluates to be true, therefore, min
is assigned the value m, i.e., 1.
Conditional Operators

30.  This operator allows the evaluation of
multiple expressions, separated by the
comma, from left to right in order and the
evaluated value of the rightmost expression
is accepted as the final result. The general
form of an expression using a comma
operator is
 Expression M = (expression1, expression2,
…,expression N);
 where the expressions are evaluated strictly
from left to right and their values discarded,
except for the last one, whose type and value
determine the result of the overall
Comma Operator

31.  C provides a useful operator, sizeof, for calculating the size of an
data item or type. It takes a single operand that may be a type name
(e.g., int) or an expression (e.g.,100) and returns the size of the
specified entity in bytes .The outcome is totally machine-dependent
For example:
sizeof Operators

32.  Evaluation of an expression in
C is very important to
understand. Unfortunately
there is no ‘BODMAS’ rule in C
language as found in algebra.
 The precedence of operators
determines the order in which
different operators are
evaluated when they occur in
the same expression.
Operators of higher
precedence are applied before
operators of lower
precedence.
Expression Evaluation:
Precedence and Associativity

33. Example: Precedence
Operator

34.  An l- value is an expression to which a value can be
assigned.
 An r- value can be defined as an expression that can be
assigned to an l- value.
 The l- value expression is located on the left side of an
assignment statement, whereas an r- value is located on
the right side of an assignment statement.
 The address associated with a program variable in C is
called its l- value; the contents of that location are its r-
value, the quantity that is supposed to be the value of
the variable.
 The r- value of a variable may change as program
execution proceeds; but never its l- value. The distinction
between l- values and r- values becomes sharper if one
l-value & r-value

35.  For example :
a = b;
b, on the right-hand side of
the assignment operator, is
the quantity to be found at
the address associated
with b, i.e., an r- value. a is
assigned the value stored
in the address associated
with b. a, on the left-hand
side, is the ad dress at
which the contents are
altered as a result of the
assignment. a is an l-
value. The assignment
operation deposits b’s r-
value at a’s l- value.
© Oxford University Press 2013. All rights reserved.
l-value & r-value

36.  Generally ,standard input and output devices
are the keyboard and the screen.
 To carry out the input and output, a number of
standard functions such as getchar(),putchar(),
scanf(), and printf() are in-built in C.
 getchar() and putchar() functions are single-
character input and output functions
respectively. So, these do not need any
formatted inputs or outputs.
 The functions scanf() and printf() handle
multiple variables of all the allowed data types in
Input and Output

37.  Non-formatted input and output can be carried out by
standard input-output library functions in C. These can
handle one character at a time. For the input functions it
does not require <Enter> to be pressed after the entry
of the character.
 A number of functions provide for character-oriented
input and output. The declarations format of two of these
are given as follows:
int getchar(void);(function for character input)
int putchar(int c);(function of character output)
Non-formatted I/O

38.  getchar() is an input function that reads a single
character from the standard input device,
normally a keyboard.
 putchar() is an output function that writes a
single character on the standard output device,
the display screen.
 There are two other functions, gets() and puts(),
that are used to read and write strings from and
to the keyboard and the display screen
respectively. A string may be defined as an
arranged collection of characters.
Non-formatted I/O function

39.  When input and output is required in a specified format
the standard library functions scanf() and printf() are
used.
 The scanf() function allows the user to input data in a
specified format. It can accept data of different data
types .
The printf() function allows the user to output data of
different data types on the console in a specified
format.
 The format string in printf(), enclosed in quotation
marks, has three types of objects:
 Ordinary characters: these are copied to output,
 Conversion specifier field: denoted by % containing
Formatted I/O function

40. Format specifiers for
printf()

41. Example

42. Example

43.  The scanf() function works in much the same way as the
printf(). It has the general form :
scanf(“control_string”,variable1_address,variable2_
address,..);
 In scanf(), the control string or format string, that
consists of a list of format specifiers, indicates the
format and type of data to be read in from the standard
input device, which is the keyboard, for storing in the
corresponding address of variables specified.
 There must be the same number of format specifiers
and addresses as there are input fields.
 scanf() returns the number of input fields successfully
scanned, converted, and stored.
 If scanf() attempts to read end-of-file, the return value is
EOF. If no fields were stored, the return value is 0.
Input function: scanf()

44.  1.The scanf() function returns the number
of variables successfully read in.
 2. The printf() function returns a number
that is equal to the number of characters
printed.
scanf() vs. printf()

45. CONTROL STATEMENTS
Selection
Statements
• if
• if-else
• switch
Iteration
Statements
• for
• while
• do-while
Jump
Statements
• goto
• break
• continue
• return

46. CONTROL STATEMENTS
Program Control
Statements/Construct
s
Selection/Branching
Conditional
Type
if
if-
else
if-
else-
if
switc
h
Unconditional
Type
break continu
e
goto
Iteration/Loopin
g
for while
do-
while

47. Operators for Control
Statements
Operators
<
>
<=
>=
!=
==
||
&&
!

48. Points to Note
 If an expression, involving the relational operator, is
true, it is given a value of 1. If an expression is false, it
is given a value of 0. Similarly, if a numeric expression
is used as a test expression, any non-zero value
(including negative) will be considered as true, while a
zero value will be considered as false.
 Space can be given between operand and operator
(relational or logical) but space is not allowed between
any compound operator like <=, >=, ==, !=. It is also
compiler error to reverse them.
 a == b and a = b are not similar, as == is a test for
equality, a = b is an assignment operator. Therefore, the
equality operator has to be used carefully.
 The relational operators have lower precedence than all
arithmetic operators.

49. Selection Statements
 One-way decisions using if statement
 Two-way decisions using if-else statement
 Multi-way decisions
 Dangling else Problem

50. One-way decisions using if statement
Flowchart for if construct
if(TestExpr)
stmtT; T F
TestExpr
stmtT

51. Example : if
Algorithm C Program
1. START #include <stdio.h>
int main()
{
int a, b, c, max;
printf(“nEnter 3 numbers”);
scanf(“%d %d %d”, &a, &b, &c);
max=a;
if(b>max)
max=b;
if(c>max)
max=c;
printf(“Largest No is %d”, max);
return 0;
}
2. PRINT “ENTER THREE
NUMBERS”
3. INPUT A, B, C
4. MAX=A
5. IF B>MAX THEN MAX=B
6. IF C>MAX THEN MAX=C
7. PRINT “LARGEST
NUMBER IS”, MAX
8. STOP

52. Flowchart of if-else construct
The form of a two-way decision
is as follows:
if(TestExpr)
stmtT;
else
stmtF;
TestExpr
stmtT stmtF
two-way decisions using if-else
statement

53. if-else-if ladder General format of switch
statements
if(TestExpr1)
stmtT1;
else if(TestExpr2)
stmtT2;
else if(TestExpr3)
stmtT3;
.. .
else if(TestExprN)
stmtTN;
else
stmtF;
switch(expr)
{
case constant1: stmtList1;
break;
case constant2: stmtList2;
break;
case constant3: stmtList3;
break;
………………………….
………………………….
default: stmtListn;
}
Multi way Decisions

54. Flowchart of an if-else-if Construct
TestExpr
TestExpr2
TestExprN
TestExpr3
stmtT2
stmtTN
stmtT3
stmtTF
stmtT1

55. Nested if
 When any if statement is
written under another if
statement, this cluster is
called a nested if.
 The syntax for the nested
is given here:
Construct 1 Construct 2
if(TestExprA)
if(TestExprB)
stmtBT;
else
stmtBF;
else
stmtAF;
if(TestExprA)
if(TestExprB)
stmtBT;
else
stmtBF;
else
if(TestExprC)
stmtCT;
else
stmtCF;
Nested if

56. A program to find the largest among three
numbers using the nested loop
#include <stdio.h>
int main()
{
int a, b, c;
printf(“nEnter the three
numbers”);
scanf(“%d %d %d”, &a, &b, &c);
if(a > b)
if(a > c)
printf(“%d”, a);
else
printf(“%d”, c);
else
if(b > c)
printf(“%d”, b);
else
printf(“%d”, c);
return 0;
}

57.  This classic problem occurs
when there is no matching else
for each if. To avoid this problem,
the simple C rule is that always
pair an else to the most recent
unpaired if in the current block.
Consider the illustration shown
here.
 The else is automatically paired
with the closest if. But, it may be
needed to associate an else with
the outer if also.
Dangling else Problem

58.  Use of null else
 Use of braces to
enclose the true
action of the
second if
With null
else
With braces
if(TestExprA)
if(TestExprB)
stmtBT;
else
;
else
stmtAF;
if(TestExprA)
{
if(TestExprB)
stmtBT;
}
else
stmtAF;
Solution to Dangling Else Problem

59. The C switch construct
The general format of a switch
statement is
switch(expr)
{
case constant1: stmtList1;
break;
case constant2: stmtList2;
break;
case constant3: stmtList3;
break;
………………………….
………………………….
default: stmtListn;
}
The Switch Statement

60. Switch Vs. Nested if
 The switch differs from the else-if in that
switch can test only for equality, whereas the
if conditional expression can be of a test
expression involving any type of relational
operators and/or logical operators.
 A switch statement is usually more efficient
than nested ifs.
 The switch statement can always be replaced
with a series of else-if statements.

61.  A loop allows one to
execute a statement or
block of statements
repeatedly. There are
mainly two types of
iterations or loops –
unbounded iteration or
unbounded loop and
bounded iteration or
bounded loop.
 A loop can either be a pre-
test loop or be a post-test
loop as illustrated in the
diagram.
Iteration & Repetitive Execution

62. Expanded Syntax of “while” and its Flowchart
Representation
while statement is a
pretest loop. The basic
syntax of the while
statement is shown
below:
“While” Construct

63. An Example
#include <stdio.h>
int main()
{
int c;
c=5; // Initialization
while(c>0)
{ // Test Expression
printf(“ n %d”,c);
c=c-1; // Updating
}
return 0;
}
This loop contains all the
parts of a while loop. When
executed in a program, this
loop will output
5
4
3
2
1
An Example

64. “for” Construct
 The general form of the for statement is
as follows:
for(initialization; TestExpr; updating)
stmT;

65. An Example
#include <stdio.h>
int main()
{
int i,n;
printf(“Enter the number”);
scanf(“%d”,&n);
for(i = 0; i < n; i++)
printf(“ %dn”,i);
return 0;
}
This loop contains all the
parts of a for loop. When
executed in a program, this
loop will output
0
1
2
3
4
An Example

66. The C do-while loop
The form of this loop
construct is as
follows:
do
{
stmT; /* body of
statements would be
placed here*/
}while(TestExpr);
“do-while” Construct

67. Point to Note
With a do-while statement, the body of the
loop is executed first and the test
expression is checked after the loop body
is executed. Thus, the do-while statement
always executes the loop body at least
once.

68. An Example
#include <stdio.h>
int main()
{
int n = 5;
do
{
printf(“HELLO”);
n++;
}while(n <= 5);
return 0;
}
This loop contains all the
parts of a do-while loop.
When executed in a
program, this loop will
output
HELLO
An Example

69. The control is
unconditionally
transferred to the
statement associated
with the label specified in
the goto statement. The
form of a goto statement
is
goto label_name;
The following program is used
to find the factorial of a
number.
#include <stdio.h>
int main()
{
int n, c, f=1;
printf(“n Enter the number:”);
scanf(“%d”,&n);
if(n<0)
goto end;
for(c=1; c<=n; c++)
f*=c;
printf(“n FACTORIAL IS %d”, f);
end:
return 0;
}
goto Statement

70. SPECIAL CONTROL STATEMENTS
 “return” statements
 “break” statements
 “continue” statements

71. return statement
 The return type is used in the definition of
a function to set its returned value and the
return statement is used to terminate
execution of the function.
 Syntax
 return;
 return expression;

72. “break” & “continue” statements
break continue
1. It helps to make an early
exit from the block where it
appears.
1. It helps in avoiding the
remaining statements in a
current iteration of the loop
and continuing with the next
Iteration
2. It can be used in all control
statements including switch
construct.
2. It can be used only in loop
constructs.

73. #include<stdio.h>
int main()
{
int c = 1;
while(c <= 5)
{
if(c == 3)
break;
printf(“t%d”, c);
c++;
}
return 0;
}
Output: 1 2
#include<stdio.h>
int main()
{
int c = 1;
while(c <= 5)
{
if(c == 3)
continue;
printf(“t%d”, c);
c++;
}
return 0;
}
Output: 1 2 4 5

74.  A nested loop refers to a
loop that is contained
within another loop.
 If the following output has
to be obtained on the
screen
1
2 2
3 3 3
4 4 4 4
then the corresponding
program will be
#include <stdio.h>
int main()
{
int row, col;
for(row=1;row<=4;++row)
{
for(col=1;col<=row;++col)
printf(“%d t”, row);
printf(“n”);
}
return 0;
}
Nested Loops