C PROGRAMMING UNIT 2

1. C-Programming
Unit-II

2. INDEX
 Operators
 Operator Precedence and assosiativity
 Evaluating expressions
 Selection and making decisions
 Two way Selection
Multiway Selection
 Repetition
Concept of Loop
Pre-test and Post-test loops
Initializing and updating
Event Counter Controlled Loops
Loops in C
Statements related to looping
 Looping Applications
Summation
Powers
Smallest and Largest Programming Examples

3. EXPRESSIONS IN C
 An expression is a sequence of operands and operators that reduces into a single
value.
 Expressions can be simple or complex.
 An Operator is a syntactical token that represents the action to be taken.
 An Operand is an object on which operation is performed.
 A simple expression contains only one operator. Example : 2+5.
 A complex expression contains more than one operator. Example: 2+5*4.
 To evaluate a complex expression we divide it into several simple expressions.
 The order in which operators in a complex expression are evaluated is determined by a
set of priorities known as Operator Precedence.
 Simple expressions are divided into six categories based on the operator precedence
,number of operands and relative positions of operator and operand.

5. Primary Expressions:
 Primary Expression contains only one operand with no operator.
 In c, operand is primary expression can be a name, a constant or a parenthesized expression.
 Null operator in this expression has precedence.
 Names, literal constants, Parenthesized expressions are categories of Primary expressions.
Names:
 A name is any identifier for a variable, a function or any other object in the language.
Examples: A B12 PRICE CALC INT_MAX
Literal Constants:
 A constant is a piece of data whose value cannot change during the execution of the program.
Examples: 5 123.5 ‘A’ “Welcome”
Parenthetical Expressions:
 A value enclosed in parenthesis must be reducible to single value and is therefore a primary
expression.
 These may include any complex expression when they are enclosed in parenthesis.
Examples: (2*3+4) (a=2*b+6)

6. Postfix Expressions
 The postfix expression consists of one operand followed by one operator.
 Function call, postfix increment and post fix decrement and various kinds of postfix
expressions.
Function call:
 Function calls are postfix expressions.
 The function name is operand and the operator is parenthesis followed by name.
 The parenthesis may contain arguments or be empty. When arguments are present they
are part of the operator.
Postfix increment or decrement:
 The postfix increment or decrement are also postfix operators.
 In the postfix increment (a++) the variable is increased by 1.
 Thus a++ results in the variable a being increased by 1 same as a=a+1.
 The postfix decrement (a--) also has a value where the value of a is decremented by 1.

7. Prefix Expressions:
 In prefix expressions, the operator comes before the operand.
Prefix increment/Decrement:
 The operand of a prefix expression must be a variable.
 With the prefix operators, the effect takes place before the expression that contains
the operator is evaluated.
 Reverse of the postfix operation.
 The effect of both postfix and prefix operations are same.

9. Unary Expressions:
 A unary expression like a prefix expression consists of one operator followed by one
operand.
 Unary expression can have an expression or a variable as operand.
sizeof:
 The sizeof operator returns us the size , in bytes of a type or a primary
expression.
 By specifying the size of an object during execution, we make our program
more portable to other hardware.
Example: sizeof(int)
 It is also possible to find the size of a primary expression.
Example: sizeof -345.23
sizeof x

10. Unary Plus/Minus:
 The unary plus and unary minus operators can be used to compute the arithmetic
value of an operand.
 The plus operator does not change the value of expression. If the expression is
negative it remains negative.
 Minus operator change the value algebraically.
Cast Operator:
 The cast operator converts one expression type to another.
 For example , to convert an integer into a real number, we would use:
float(x)
 With unary operators, only the expression value is changed. Integer variable x is
unchanged.

11. Binary Expressions:
 Binary expressions are formed by an operand-operator-operand combination.
 Any two numbers added, subtracted, multiplied or divided are usually formed in algebraic notation which is a binary
expression.
Multiplicative Expression:
 The result of multiply operator(*) is product of the two operands..
 The operands can be any arithmetic type (integral or floating point)
 The result of a divide(/) operator depends on the type of the operands.
 If one or both operands is of floating point type, the result is floating point quotient.
 If both operands are integral type, the result is integral part of the quotient.
 Modulo (%) operator divides the first operand by second operand and returns the remainder rather than the
quotient.
 Both operands must be integral type and the operator returns the remainder as an integer type.
10 % 3 //evaluates to 1
true % 4 //evaluates to 1
‘A’ % 10 // evaluates to 5
22.3 % 2 //Error: Modulo cannot be floating point.

12. Additive Expressions:
 In additive expressions, the second operand is added to or subtracted from the first operand, depending on the operand
used.
 The operands in an additive expression can be any arithmetic types (integral point or floating point).
 Additive operators have lower precedence than multiplicative operators .
Assignment Expressions:
 The assignment expression evaluates the operand on the right side of the operator (=) and places it’s value in the variable on
the left .
 The assignment expression has a value in variable on the left.
 The value of the expression is the value on the right of assignment operator.
 The side effect places places the expression value in the variable on the left of assignment operator.
 There are two forms of assignment: simple and compound.
Simple assignment:
 The simple assignment is found in algebraic expressions.
a=5 b=x+1 i=i+1
Compound assignment:
 A compound assignment is a shorthand notation for a simple assignment .It requires that the left operand be repeated as a
part of right expression. Some of compound expressions: *=,/=,%=,+=,-=.
Compound expression x*=y+3 is evaluated as: x=x*(y+3)

13. Types of Operators in C:

14. C - Operators
 An operator is a symbol that tells the compiler to perform specific mathematical or
logical functions. C language is rich in built-in operators and provides the following
types of operators −
1.Arithmetic Operators
2.Relational Operators
3.Logical Operators
4.Bitwise Operators
5.Assignment Operators
6.Misc Operators

15. Arithmetic Operators
erator

16. Relational Operators

17. Logical Operators

18. Bitwise Operators

22. Ternary Expressions:
 Ternary expressions contains a condition followed by two statements or values.
 If condition is true the first statement is executed otherwise second statement.
 Conditional Operators are sometimes called ternary operators because they take three arguments
 Syntax: Condition ? (expression 1) : (expression 2) :
 Two expressions are separated by a colon. If condition is true expression1 gets evaluates
otherwise expression2 . The condition is always written before ? Mark.

23. Operator Precedence and associativity:
 Precedence is used to determine the order in which different operators in a complex
expression are evaluated.
 Associativity is used to determine the order in which operators with same precedence
evaluated in the same expression.
 The concept of precedence explains the priority in performing various operations.
 Simple example of precedence:
2+3*4
 The above expression is actually two binary expressions with one addition and one
multiplication operator.
Precedence of multiplication operator is higher compared to precedence of addition
operator. This results in evaluating multiplication first and then addition.

24. Associativity :
 Associativity can be left to right or right to left.
 Left to right associativity evaluates expression by starting on left and moving to right.
 Example: 3*8/4%4*5
In the above expression we have four operators of same precedence.
 Associativity describes how sub expressions are grouped together .
 Since their associativity is from left to right they are grouped as follows:
((((3*8)/4)%4)*5)3
 Right to left associativity occurs when more than one assignment operator occurs in an
assignment expression.
 The assignment operators must be interpreted from right to left.(right most expression
evaluates first.) then it’s value will be assigned to the operand on left of the assignment
operator .
 Example: a+=b*=c-=5
 (a+=(b*=(c-=5))
(a=a+(b=b*(c=c-5)))

26.  Side effects: A side effect is an action that results from the evaluation of an expression . C first
evaluates the expression on the right of assignment operator and then places the value in the left
variable.
 Value of the left variable changes once operator on the right side of expression evaluates.
Evaluating Expressions:
 To evaluate expressions with out side effects we need to follow rules as mentioned below:
 Replace the variables by their values
 Evaluate the highest precedence operators and replace them with the resulting
value.
 Repeat step 2 until the result is a single value.
 To evaluate the expression with side effects ie, parenthesized expressions we need to follow rules
as mentioned below:
 Calculate the value of parenthesized expression
 Evaluate the postfix expression
 Evaluate the prefix expression
 Then multiply and division are now evaluated using their associativity rule.
 Last step is to evaluate the subtraction.

27. Selection and making decisions in C
 Selection and making decisions in C programming includes two catregories:
1. Two way Selection
2. Multiway Selection based on the context.

28. Two- way Selection:
 The basic decision making statement in the computer is two-
way selection.
 The decision is described to the computer as a conditional
statement that can be answered either true or false.
 If the answer is true, one or more action statements are
executed.
 If answer is false then a different action or set of actions are
executed.
 Regardless of which set of actions is executed the program
continues with the next statement after the selection.

29.  C implements two way selection with if…else statement.
 An if..else statement is a composite statement used to make
decision between two alternatives.
 There are some syntactical points to be followed to implement
if…else statement:
1. The expression must be enclosed in parenthesis.
2. No semicolon is needed for an if..else statement
3. The expression can have a side effect
4. Both the true or false statements can be any
statement or a null statement.
5. Both the statements can be same. Multiple
statements can be combined into a compound
statement through use of braces.
6. We can swap the position of statement 1 and
statement 2 if we use the compliment of original
statement.

30. Null else statement:
 If the else condition is not required that is null else statement , if it is null then else can
be omitted.
 It is possible to omit the false branch but the true branch can not be omitted.
 To eliminate it we need to use rule 6 which allows us to compliment the expression
and swap two statements .
 The result is known as complemented if…else .

32.  if…else may statements may be any statements including another if…else.
 When an if..else is included within an if..else it is known as nested if statement.
 There is no limit how many levels can be nested.3

34. Multi-way Selection:
 C has two different ways to implement multiway selection.
 The first way is by using the switch statement .
 The another way is through else-if a convenient way of if elseif implementation.
 The switch statement can be used only when the selection condition reduces to an
integral expression.

35. The switch statement:
 Switch is a composite statement used to make a decision between many
alternatives.
 Although the switch expression can use any expression that reduces to an
integral value, the most common is unary expression in the form of integral
identifier.
 The selection alternatives known as case label must be C integral types.
 For every possible value in the switch expression a separate case label is
defined.
 Everything from the case label to the next case label is a sequence.
 The case label simply provides an entry point to start executing the code.
 The default label is a special form of case label . It is executed when ever none
of other case values matches the value in switch expression.

37. Rules for switch statement:
 The control expression that follows the keyword switch must be an integral type.
 Each case label is the keyword case followed by a constant expression.
 No two case labels can have the same constant expression value.
 But two case labels can be associated with the same set of actions.
 The default label is not required. If the value of expression does not match with any
labelled constant expression the control transfers outside of the switch statement .
 The switch statement can include at most one default label that can be coded any where
but it is traditionally coded last.

39.  The else-if is an artificial C construct that is
only used when
 The selection variable is not an integral
 The same variable is being tested in the
expression.

41. Repetition
Concept of loop:
 Loop is a action that is repeated over and over again .
 A loop shall be stopped when the task is done .
 To make sure that it ends, we must have a condition that controls the loop .
 That means we need to check the condition before and after execution point of each
iteration.
 If the task is not achieved then the loop will iterate until the task is done and it
terminates.

42. Pre-test and Post-test loops
 In a pretest loop, the control expression is tested first . If it is true, the loop continues
otherwise the loop is terminated.
 In posttest loop, in each iteration, the loop actions are executed then the control
expression is tested . If it is true, new iteration starts else loop terminates.

43. Initialization and Updating:
 Before a loop can start, we need to declare where the loop need to start.
 Such declaration is called initialization.
 Initialization can be done before the first execution of the loop body.
 It sets the stage for loop actions.
 Initialization can be explicit or implicit.
 When the initialization is explicit, we include code to set the beginning values of key loop
variables.
 Implicit initialization provides no direct initialization code , it rather relies on a pre-existing
situation to control the loop.
Loop Update:
 The actions that cause changes to values to the initialized declarations , such changes are called
loop update.
 Updating is done in each iteration , usually as the last action.
 If the body of the loop is repeated m times, then the updating is done m times.

45. Event and Counter-Controlled loops:
Event – Controlled loops:
 In an event – controlled loop, an event changes the control expression from true to false.
 When reading data , reaching the end of the data changes the expression from true or false.
 In event – controlled loops, the updating process can be implicit or explicit.
 If it is explicit, such as finding piece of information , it is controlled by the loop.
 If it is implicit, it is controlled by external condition.
Counter – Controlled Loops:
 When we know the number of times an action is to be repeated, we use a counter controlled loop.
 We must initialize, update and test the counter.
 Although we need to know the number of times we want to execute the loop, the number need not be a
constant.
 It can also be a variable or a calculated value.
 The update can be increment in case where we are counting up and decrement when we are counting down.
Loop Comparison:
 The number of iterations of a loop is given as n.
 In a pre-test loop, when we come out of the loop, the limit test has been executed n+1 times.
 In a post-test loop, when we come out of the loop, the limit test has been executed only n times.

46. Loops in C
 C has three loop statements : the while , the for and the
do-while.
 The while and the for loops are pretest loops and do-while
is posttest loop.
 While and do-while event controlled loops and for is counter
controlled loops.

47. The while-loop:
 The while loop is a pretest loop
 It uses an expression to control the loop.
 As it is a pretest loop, it tests the expression before every iteration of the
loop.
 No semicolon is needed at the end of while statement
 If we want to include multiple statements in the body, we must put them in a
compound statement block.

50. The for loop:
 The for statement is a pretest loop that uses three expressions .
 The first expression contains any initialization statement.
 The second expression contains limit-test.
 The third expression contains updating expression.
 Expression 1 is executed when the for starts .
 Expression 2 is tested before each iteration .
 Since the for loop is a pretest loop, the body of for loop is not
executed if the limit condition is false at the start of loop.
 Expression 3 which is update expression is executed at the end of
each loop .
 C allows the limit test in Expression 2 to be a variable.
 The value of variable shall be changed during the execution of
loop.
 If for loop must be executed as a compound statement if for loop
includes more than one statement.

53. The do…while loop:
 The do…while statement is a post-test loop.
 It uses an expression to control the loop, but it tests the expression / condition after the
execution of the body.
 The body of do…while loop must be one and only one statement.
 If we need to include multiple statements in the body of loop we must code them inside
the compound statement.
 Do….while loop is implemented while data validation.

56. The Comma expression:
 A comma expression is a complex expression made of two expressions separated by
commas
 Such kind of expressions are mostly used in for statements.
 The expressions are evaluated from left to right.
 The value and type of the expressions are the value and type of the right expression.
 The comma expression has the lowest priority of all expressions.

58. Other statements related to looping:
 break, continue statements are related to are other statements related to looping.
break
 In a loop, the break statement causes a loop to terminate.
 If a code includes a series of nested loops, break statement terminates only the innerloop.
 break statement needs a semicolon
 break statement can be used in any of the looping statements while, do .. while and for
loops and can be used in switch condition.
continue
 The continue statement does not terminate the loop but simply transfers to testing
expression in while and do .. while.
 The use of continue statement can also be considered as unstructured programming.

60. Looping Applications:
 Summation , product, smallest or largest are common applications of loops.
 A common design runs through all the looping statements .
 With few exceptions, each loop contains initialization code , looping code,
and disposition code

61. Summation:
 When we need to add many numbers or a variable series of numbers we can use the
add operator in a loop.
 A sum function has three logical parts: (i)initialization of any necessary working
variables (ii) the loop which includes summation code and any data validation code
and (iii) the disposition code to print or return the result.
 In each loop we read the next number and add it to the accumulator
 A similar application of counting , is a special case of summation in which we add 1 to
the counter instead of adding the number we read to the accumulator.

64. Powers
 A product loop is useful for two common applications: raising a number to a
power and calculating the factorial of a number
 Notice that this includes initialization logic to validate the parameter list.
 If either of the parameters is invalid , we return zero an error indicator.
 For product based applications, such as powers we must initialize it to 1.

67. Smallest and largest
 We often encounter a situation we must determine the smallest or
larget among a series of data.
 This is also called a natural looping structure.
 Each iteration then tests the current smallest to the next number.
 If this new number is smaller than the current smallest , we replace
the smallest.
 To find the smallest of a series , the initialization sets the initial
value of smallest to the largest.
 The loop then proceeds to read a series of numbers and tests each
once against previously stored smallest number.
 Since the smallest number starts with maximum integer value, the
first number automatically becomes smallest.
 Therefore the result entirely depends on data being read. And
returns smallest number.
 To find the largest number, we need to initialize smallest variable to
a very small number.
 To find the largest number, we need to initialize the result to a very
large number.