Manzoor alam studying aat uet peshawar

1. 1
Control Structures

2. 2
Flow chart
 Graphical representation of an algorithm or a portion of algorithm.
 Drawn using certain special-purpose symbols connected by arrows
called flow lines.
 Special purpose symbols.
Following are some symbols to draw a flow chart and there purpose.
Rectangles are action symbols to indicate any
type of action, including a calculation or an
input output operation.
Diamonds are conditional or decision symbols.
It indicates a decision to be made.
lozenges, ovals or rounded rectangles, indicate
start or end of the program usually containing
the word "Start, begin” or "End“.

3. 3
Flow chart
Parallelogram are the input/output symbols
Arrows, showing what's called "
flow of control“. An arrow coming from
one symbol and ending at another
symbol represents that control passes to
the symbol the arrow points to. Arrows
are also called flow lines.

4. 4
Control structures

Control structure
 A control statement and the statements whose execution it controls.
 a control statement is any statement that alters the linear flow of
control of a program. C++ examples include: if-else, while, for, break,
continue and return statement
 Sequential execution
 Statements executed in order
 Transfer of control
 Next statement to be executed may be other than the next one in
sequence.

5. 5
Control structures
 Bohm and Jacopini’s control structures
Bohm and Jacopino’s work demonstrate that all programs could be written in
terms of only three control structures.
Sequence structures, selection structures and repetition structures.
 Sequence structure
 Built into C++. Programs executed sequentially by default.
 Selection structures

C++ has three types - if, if/else, and switch

6. 6
Control structures
 if selection structure
. Perform an action if condition is true.
. Skip the action if condition is false.
 If/else selection structure
. Perform an action if condition is true.
. Performs a different action if the condition is false.
 switch selection structure
. Perform one of many different actions depending on the value of an
integer expression.

7. 7
Control structures
 Repetition structures
 Many application require certain operations to be carried out more
than once. Such situations require repetition in control flow.
 C++ has three types while, do/while, for
 While selection structure
. An action to be repeated while some conditions remains true.
 Do/While selection structure
. Similar to while structure.
. Tests the loop continuation after the loop body is performed.
. while structure the loop continuation condition is tested at the beginning
of the loop before the body of loop is performed.
 We are going to discuss if and if/else selection structures first and
will explain the repetition structures and switch selection structure
latter. It was just an introduction to these structures.

8. 8
Decision making structure/ selection structure
 Selection structure/decision structure
 allows the program to make a decision or comparison and then
select one of two paths, depending on the result of the comparison.
 Condition
 condition” is a logical expression that evaluates to true or false. It
could be a relational or Boolean expression. In other words
 Specifies the decision you are making
 Must result in either a true or false answer
 IF Structure
 One statement or a block of statement enclosed in braces {}
i.e. (compound statement), to be processed If condition met
otherwise it is skipped.

Uses equality and relational operators

9. 9
Equality and relational operators
 Conditions in if structures can be formed by using the equality
and relational operators
 Equality operators
 Same level of precedence
 Associated left to right.
 Relational operators
 Same level of precedence.
 Associated left to right.
 Equality operators precedence is lower then precedence of
relational operators.

10. 10
Equality and relational operators
Standard algebraic
equality operator or
relational operator
C++ equality
or relational
operator
Example
of C++
condition
Meaning of
C++ condition
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
Equality operators
= == x == y x is equal to y
≠ != x != y x is not equal to y

11. 11
Boolean Expressions
 Boolean expressions are expressions that are
either true or false
 comparison operators such as '>' (greater than)
are used to compare variables and/or numbers
 (grade >= 60) Including the parentheses, is the
boolean expression from the grade example
 A few of the comparison operators that use two
symbols (No spaces allowed between the symbols!)
 > greater than
 != not equal or inequality
 == equal or equivalent
 <= less than or equal to
etc

12. 12
If selection structure
 The primary C++ selection structure statement used to
perform a single-alternative selection.
 Choose among alternative courses of action
 If the condition is true
 statement Print statement executed, program continues to
next
 If the condition is false
 Print statement ignored, program continues

13. 13
If selection structure flow chart

14. 14
If selection structure
 example:
Pseudocode
If student’s grade is greater than or equal to 60
Print “Passed”
C++ code
if ( grade >= 60 )
cout << "Passed";

15. 15
If selection structure
 Flow chart for the pseudocode statement.
true
false
grade >= 60 print “Passed”
A decision can be made on
any expression.

16. 16
Example
 Example is using the relational and equality operators.
 Following example used six if statements to compare two numbers
input by the user.
 If the condition in any of these if statements is satisfied, the
output statement associated with if is executed.
 If the condition with the if statement is false the output statement
associated with that if statement is skipped.
 Observe the different outputs for various inputs at the end of the
program.

17. 17
1 // example
2 // Using if statements, relational
3 // operators, and equality operators
4 #include <iostream.h>
5
6
7
8
9
10 int main()
11 {
12 int num1, num2; // declare variables
13
14 cout << "Enter two integers, and I will tell youn"
15 << "the relationships they satisfy: ";
16 cin >> num1 >> num2; // read two integers
17
18 if ( num1 == num2 )
19 cout << num1 << " is equal to " << num2 << endl;
20
21 if ( num1 != num2 )
22 cout << num1 << " is not equal to " << num2 << endl;
23
24 if ( num1 < num2 )
25 cout << num1 << " is less than " << num2 << endl;
26
27 if ( num1 > num2 )
28 cout << num1 << " is greater than " << num2 << endl;
29
30 if ( num1 <= num2 )
31 cout << num1 << " is less than or equal to "
32 << num2 << endl; //continued on next slide
33
if structure compares values
of num1 and num2 to test for
equality.
If condition is true (i.e.,
values are equal), execute this
statement.if structure compares values
of num1 and num2 to test for
inequality.
If condition is true (i.e.,
values are not equal), execute
this statement.
If structure compare the
values of num1 and num2 to
test if num1 is less than num2
If condition is true (i.e., num1
is less than num2 ), execute
this statement.if structure compares values
of num1 and num2 to test if
num1 is greater than num2
If condition is true (i.e., num1
is greater than num2 ),
execute this statement.if structure compares values
of num1 and num2 to test if
num1 is less than or equal to
num2
If condition is true (i.e., num1
is less than or equal to num2),
execute this statement.

18. 18
34 if ( num1 >= num2 )
35 cout << num1 << " is greater than or equal to "
36 << num2 << endl;
37
38 return 0; // indicate that program ended successfully
39 }
Input is 35 and 30
Input is 25 and 25
Input is 10 and 20

19. 19
If/else selection structure
 Different actions if conditions true or false
 Syntax
 A single statement for each alternative
if (Boolean_expression)
yes_statement;
else
no_statement;
 A sequence statement for each alternative
if (Boolean_expression)
{ yes_statement1;
yes_statement2;
yes_statement last; }
else
{ no_statement1;
no_statement2;
no_statement last; }

20. 20
If/else selection structure flow chart
Boolean expression
Action if false Action if true
truefalse

21. 21
If/else selection structure
Example
 Pseudocode
if student’s grade is greater than or equal to 60
print “Passed”
else
print “Failed”
 C++ code
if ( grade >= 60 )
cout << "Passed";
else
cout << "Failed";

22. 22
If/else selection structure
Flow chart for the pseudocode
truefalse
print “Failed” print “Passed”
grade >= 60

23. 23
Compound Statement
 Compound statement
 Set of statements within a pair of braces also known as
BLOCK
if ( grade >= 60 )
cout << "Passed.n";
else {
cout << "Failed.n";
cout << "You must take this course again.n";
}
 Without braces,
cout << "You must take this course again.n";
always executed

24. 24
Another simple Example
1. //program to determine if user is ill
2. #include <iostream>
3. using namespace std;
4. int main()
5. {
6. const double NORM = 98.6; // degree Fahranheit;
7. double temperature;
8. cout<<"Enter your temperaturet";
9. cin>>temperature;
10. if (temperature>NORM) //if temperature is greater than NORM print following statement
11. cout<<"nnYou are sickn"<<"take rest and drink lots of fluids";
12. else //if temperature is <= NORM print following statement
13. cout<<"nnYou are perfectly fine";
14. return 0;
15. }

25. 25
output
Input is 100
100 > NORM
Input is 98
98<NORM

26. 26
Example of if and if/else selection structure drawn in flow
chart form
If selection structure(program 1) If/else selection structure(program2)

27. 27
c++ code for the flow chart of if selection structure
(program 1).
1. //program 1
2. //program to find the part prices for the given part number.
3. #include<iostream>
4. using namespace std;
5. int main()
6. {
7. int part_number, ;
8. float price;
9. cout<<"enter part number"<<endl;
10. cin>>part_number;
11. cout<<"enter price"<<endl;
12. cin>>price;
13. if(part_number==203)
14. price = price*1.1;
15. cout<<"price is "<<price;
16. return 0;
17. }

28. 28
Output of program 1
Part_number is equal to 203
Part_number is not equal to 203

29. 29
c++ code for the flow chart of if/else selection structure
(program 2).
 //program to calculate the sales commission
 #include <iostream>
 using namespace std;
 int main()
 {
 float sales, commission;
 cout<<"enter the sales"<<endl;
 cin>>sales;
 if (sales>1500)
 commission = sales*0.2;
 else
 commission = sales*0.1;
 cout<<"commission is"<<commission;

 return 0;
 }

30. 30
Output of program 2
Sales is 1500
Sales is greater than 1500

31. 31
Example of if/else
 Write a program to calculate the gross pay of an employee.
 The employee is paid at his basic hourly rate for the first 40 hours worked
during a week. Any hours worked beyond 40 is considered overtime.
 overtime is paid at the 1.5 times the hourly rate.
Pseudocode
If total number of hours >40
Gross pay = rate*40 + rate*1.5(hours – 40)
Else
Gross pay = rate * hours

32. 32
C++ code
1. #include <iostream>
2. using namespace std;
3. int main()
4. {
5. int hour; //declaration
6. double gross_pay, rate;
7. cout<<"enter the hourly rate of payt"<<endl; //prompt
8. cin>>rate; //reading data
9. cout<<"enter the number of hours worked t"<<endl; //prompt
10. cin>>hour; //readin data
11. if(hour>40) //condition if working hours is greater than 40
12. gross_pay = rate*40 + 1.5*rate*(hour - 40); //gross pay including extra hour
13.
14. else //if working hour is <=40 then use this formula to get gross pay
15. gross_pay = rate*hour;
16.
17. cout<<" Gross pay is t"<<gross_pay<<endl; //printing the gross pay on screen.
18. return 0;
19. }

33. 33
output
Hour<40
Hour>40

34. 34
If/else selection structure
 Ternary conditional operator (?:)
 It is only ternary operator.
 It takes three operands together with conditional operator to form a
conditional expression
 Three arguments (condition, value if true, value if false)
 example
cout << ( grade >= 60 ? “Passed” : “Failed” );
 the value in the conditional can also be actions to execute for example
grade >= 60 ? cout << “Passed” : cout << “Failed” ;
Condition Value if true Value if false

35. 35
Nested if/else structure
 if structure that rests entirely within another if structure,
within either the if or the else clause
 One inside another, test for multiple cases
 Once condition met, other statements skipped

36. 36
Simple example to understand the nested if/else
 Consider an example of a program segment that accepts a gender
code and print gender according to that code.
 Pseudocode
if the gender code is F
print female
else
if the gender code is M
print male
else
print invalid code

37. 37
Simple example to understand the nested if/else
 Flow chart

38. 38
Simple example to understand the nested if/else
 C++ code
//F and M are correct codes
//f and m are invalid codes

39. 39
Nested if/else structure
 following pseudocode is example of nested if/else
 if student’s grade is greater than or equal to 90
Print “A”
 else
if student’s grade is greater than or equal to 80
Print “B”
else
if student’s grade is greater than or equal to 70
Print “C”
else
if student’s grade is greater than or equal to 60
Print “D”
else
 Print “F”

40. 40
Nested if/else structure
C++ code
if ( grade >= 90 ) // 90 and above
cout << "A";
else
if ( grade >= 80 ) // 80-89
cout << "B";
else
if ( grade >= 70 ) // 70-79
cout << "C";
else
if ( grade >= 60 ) // 60-69
cout << "D";
else // less than 60
cout << "F";
 if grade>=90, first four conditions will be true. But only the cout statement after the
first test will be executed. After that cout is executed, the else part of the outer
if/else statement is skipped.

41. 41
Avoiding Common Pitfalls with if Statements
 Forgetting that C++ is case sensitive
 Assuming that indentation has a logical purpose
 Adding an unwanted semicolon
 Forgetting curly braces
 Using = instead of == (explained with example on next slide)
 Making unnecessary comparisons

42. 42
Logical Operators
 Logical operators are used to combine more than one condition forming a complex
condition.
 Allow you to combine two or more conditions into one compound condition
 Data validation
 the process of verifying that the input data is within the expected
range
 C++ logical operators are
&& (Logical AND)
|| (Logical OR)
! (Logical NOT , logical negation)

43. 43
Logical Operators
 && (Logical AND)
 All of the conditions must be true for the compound condition to be
true
 Syntax (Condition_1) && (Condition_2)
 True if both expressions are true
 Example
 if ( (2 < x) && (x < 7) )
 True only if x is between 2 and 7
 Inside parentheses are optional but enhance meaning

44. 44
Logical Operators
 Be careful translating inequalities to C++
 if x < y < z translates as
if ( ( x < y ) && ( y < z ) )
NOT
if ( x < y < z )

45. 45
Logical Operators
 || (Logical OR)
 only one of the conditions must be true for the compound condition to be true
 True if either or both expressions are true
 Syntax (Condition_1) || (Condition_2)
 Example
 if ( ( x = = 1) | | ( x = = y) )
 True if x contains 1
 True if x contains the same value as y
 True if both comparisons are true

46. 46
Example to print hello according to user’s choice
Notice the program will print hello if input
Is upper case Y or lower case y

47. 47
Output
Notice that program accepts both
Lowe case y and upper case Y

48. 48
Logical Operators
 ! (Logical NOT , logical negation)
 Reverses the truth/falsity of its condition
 Returns true when its condition is false, & vice versa
 Is a unary operator, only takes one condition
 Example
if ( !( grade == sentinelValue ) )
cout << "The next grade is " << grade << endl;
Alternative
if ( grade != sentinelValue )
cout << "The next grade is " << grade << endl;

49. 49
Logical Operators
 ! negates any boolean expression
 !( x < y)
 True if x is NOT less than y
 !(x = = y)
 True if x is NOT equal to y
 ! Operator can make expressions difficult to understand…use only
when appropriate
Truth table for the ! (NOT, logical negation) operator

50. 50
Confusing Equality (==) and Assignment (=) Operators
 Common error
 Does not typically cause syntax errors
 Aspects of problem
 Expressions that have a value can be used for decision
 Zero = false, nonzero = true
 Assignment statements produce a value (the value to be
assigned)
 = Assignment operator
 Used to assign values to variables
 X = 3
 == equality operator
 Used to compare values
 If (X == 3)

51. 51
Confusing Equality (==) and Assignment (=) Operators
 Example
if ( payCode == 4 )
cout << "You get a bonus!" << endl;
 If paycode is 4, bonus given
 If == was replaced with =
if ( payCode = 4 )
cout << "You get a bonus!" << endl;
 Paycode set to 4 (no matter what it was before)
 Statement is true (since 4 is non-zero)
 Bonus given in every case

52. 52
Confusing Equality (==) and Assignment (=) Operators
 L-values
 Expressions that can appear on left side of equation
 Can be changed (I.e., variables)
 x = 4;
 R-values
 Only appear on right side of equation
 Constants, such as numbers (i.e. cannot write 4 = x;)
 L-values can be used as R-values, but not vice versa

53. 53
The switch Multiple-Selection Structure
 Switch is typically a selection structure and an alternative to the long
string of ifs
 Tests variables for multiple values
 Consists of a series of case labels and an optional default case
 General format
 switch ( variable ) {
case value1: // taken if variable == value1
statements
break; // necessary to exit switch
case value2:
case value3: // taken if variable == value2 or == value3
statements
break;
default: // taken if variable matches no other cases
statements
break;
}

54. 54
The switch Multiple-Selection Structure
 Expression (variable in braces after switch)
must be of type integer or character. It is the
controlling expression of switch statement
 The keyword case must be followed by a
constant
 break statement is required unless you want all
subsequent statements to be executed.

55. 55
Reviewing character data type
 As we know a computers can process character data too
 char
 Short for character
 Can be any single character from the keyboard
 To declare a variable of type char:
char letter;
 Character constants are enclosed in single quotes
char letter = 'a';
 Strings of characters, even if only one character
is enclosed in double quotes
 "a" is a string of characters containing one character
 'a' is a value of type character

56. 56
char   int
 It is possible to store char values in integer variables (an important feature of c++)
 Characters are represented as 1-byte integer in computers so we can treat a
character as either char or int depending on its use
int value = ‘A'; //65 is ASCII for A
 value will contain an integer representing 'A‘ i.e. value = 65
 Similarly
 It is possible to store int values in char variables
char letter = 97; //97 is numerical representation of lower case a (ASCII)
 Result of the above statement is letter = a
 Use single quotes to get numerical representation of a character
cout << "The character (" << 'a' << ") has the value "
<< ( int ) ( 'a' ) << endl;
Prints
The character (a) has the value 97
ASCII (American Standard Code For Information Interchange)

57. 57
Comparing if/else with switch with the help of an example
•When you want to create
different outcomes
depending on specific
values, you can use a series
of ifs.

58. 58
Comparing if/else with switch with the help of an example
 However, as an alternative to the long string of ifs, you can use the switch
statement
 Department is the control variable and is integer
 Compare the department to cases and prints the department it matches.
Removing break changes behavior of
statement.
It causes switch statement to end.

59. 59
Example problem
 Problem statement
 Write a c++ program that enters the students grades
represented by letters A, B, C, D and F (program should
not be case sensitive)
 Use switch to count the number of each different letter
grades that the student earned on an exam
 Observe the flow chart on the next slide

60. 60
Flow chart
true
false
.
.
.
case a case a action(s) break
case b case b action(s) break
false
false
case z case z action(s) break
true
true
default action(s)

61. 61
C++ code
1 // grades are represented by letters
2 // Counting letter grades.
3 #include <iostream>
4
5
9 // function main begins program execution
10 int main()
11 {
int grade; // one grade
//initializing and declaring counters
13 int aCount = 0; // number of As
14 int bCount = 0; // number of Bs
15 int cCount = 0; // number of Cs
16 int dCount = 0; // number of Ds
17 int fCount = 0; // number of Fs
18
19 cout << "Enter the letter grades." << endl
20 << "Enter the EOF character to end input." << endl;
21

62. 62
C++ code
22 // loop until user types end-of-file key sequence
23 while ( ( grade = cin.get() ) != EOF ) {
24
25 // determine which grade was input
26 switch ( grade ) { // switch structure nested in while
27
28 case 'A': // grade was uppercase A
29 case 'a': // or lowercase a
30 ++aCount; // increment aCount
31 break; // necessary to exit switch
32
33 case 'B': // grade was uppercase B
34 case 'b': // or lowercase b
35 ++bCount; // increment bCount
36 break; // exit switch
37
38 case 'C': // grade was uppercase C
39 case 'c': // or lowercase c
40 ++cCount; // increment cCount
41 break; // exit switch
42
cin.get() This function gets 1
character from the keyboard (after Enter
pressed), and it is assigned to grade.
Variable grade is the controlling
expression of switch. Value of grade is
compared with each of the case label
break causes switch to end and the
program continues with the first statement
after the switch structure.
If break is not used in switch structure each
time the match occur, statement for all
remaining cases will be executed.
Compares grade (an int) to the
numerical representations of A
and a.
cin.get() returns EOF (end-of-file) after the EOF
character is input, to indicate the end of data.
If the value assigned to grade is EOF the program
terminates.
EOF is symbolic integer constant defined in
<iostream> header file
EOF may be ctrl-d (UNIX) or ctrl-z (DOS, MS)
depending on your OS.

63. 63
C++ code
43 case 'D': // grade was uppercase D
44 case 'd': // or lowercase d
45 ++dCount; // increment dCount
46 break; // exit switch
47
48 case 'F': // grade was uppercase F
49 case 'f': // or lowercase f
50 ++fCount; // increment fCount
51 break; // exit switch
52
53 case 'n': // ignore newlines,
54 case 't': // tabs,
55 case ' ': // and spaces in input
56 break; // exit switch
57
58 default: // catch all other characters
59 cout << "Incorrect letter grade entered."
60 << " Enter a new grade." << endl;
61 break; // optional; will exit switch anyway
62
63 } // end switch
64
65 } // end while
66
This test is necessary because
Enter is pressed after each
letter grade is input. This adds
a newline character that must
be removed. Likewise, we
want to ignore any
whitespace.
Notice the default statement, which
catches all other cases.
If no match occurs, the default case is
executed and an error message is
printed

64. 64
C++ code
67 // output summary of results
68 cout << "nnTotals for each letter grade are:"
69 << "nA: " << aCount // display number of A grades
70 << "nB: " << bCount // display number of B grades
71 << "nC: " << cCount // display number of C grades
72 << "nD: " << dCount // display number of D grades
73 << "nF: " << fCount // display number of F grades
74 << endl;
75
76 return 0; // indicate successful termination
77
78 } // end function main

65. 65
Output