Fundamentals of Computer Programming - Flow of Control I

Jan 2023
FUNDAMENTALS OF COMPUTER
PROGRAMMING
Chere L. (M. Tech)
Lecturer, SWEG, AASTU
Using C++

Jan 2023
PROGRAM FLOW CONTROLS
(Selection Statements)
Outline
▪ Introduction to flow control
▪ Branching flow controls
✓ One-way selection
✓ Two-way selection
✓ Multiple selections
✓ switch statement
CHAPTER FOUR

Jan 2023
Objectives
At the end of this section, you able to
▪ Identify and use selection flow controls
▪ Form and evaluate Boolean expressions
▪ Examine the relational and logical operators
▪ Write a program using selection statements

Jan 2023
4.1 Introduction to Flow Control

Jan 2023
What is flow control?
▪ It refers to the order in which a program statements (instructions) are
executed (performs actions).
▪ The term reflects the fact that the currently executing statement has
control of the CPU and is handed over (flow) to another statement when
its execution is completed.

Jan 2023
Cont’d
The natural flow control of program
▪ Typically, the flow control in a program is
sequential, which is the most common and
straightforward.
▪ However, usually a program execution is not
limited to a sequential

Jan 2023
Cont’d
Can the programmer
alter the normal
order of program
execution?
▪ Yes, programmers can control the order of
instruction execution
▪ Accordingly, most programming language
including C++ provides control structures that
serve to specify what has to be done by our
program, when and under which circumstances.

Jan 2023
The Basic Program Flow Controls
▪ Generally there are three basic program flow controls
Execution of instructions
sequentially one after
another
allow alternative actions
based upon conditions that
are evaluated at run time
allows to execute a
statement or group of
statements multiple times

Jan 2023
Logical/Boolean expressions
What are Logical/Boolean expressions?
▪ Refers to the expressions that are evaluated as true/false
▪ Formed using the logical or/and relational operators
(refer to Operator and expression topic for the details)
▪ Logical/Boolean expressions are a fundamental part of control statements
Example of
a Boolean
expression

Jan 2023
Summary
In this section, we briefly discussed;
➢ Program flow control concept
➢ Revision on relational and logical operators
➢ Formation and evaluation of Logical/Boolean expressions

Jan 2023
4.2 Selection Statements
(if … else statements)

Jan 2023
Types of Selection Statements
▪ Selection statements include
✓ One-way selection ----> if statement
✓ Two-way selection statements
➢ if...else statement
➢ Conditional operator
➢ nested if --- else statement
✓ Multiple selection statements
➢ else if…else statement
➢ Switch statement

Jan 2023
I) if Statement (single-selection)
▪ Syntax
if (expression) {
statement (s);
}
next statement(s);

Jan 2023
Cont’d
When to use it?
▪ When there is a one-time condition check in the program and the
program continues with the normal execution either the condition is
satisfied or not.
Example:
▪ Computing salary bonus for an employee given extra hours worked.
▪ Set the nth bit of a long integer num to 1

Jan 2023
Exercise 4.1
Problem description
Write a C++ program to calculate the Net-Pay of an employee as follow after deduction
of pension (7%) and tax. The program should read the gross salary, worked hours, and
income tax rate. If the employee worked hours exceed 40 hrs., the program prompts
the user to enter an over-time bonus rate/hour and find the bonus payment by
multiplying the extra hours worked with the provided bonus rate.
net Salary = (gross Salary – pension – income tax) + Overtime payment
Purpose: To demonstrate the use case of the if statement.

Jan 2023
Solution
(Problem Analysis)
Input
- employee gross salary,
- worked-hours,
- income tax rate,
- the bonus rate
Output
- Employee Net salary
Process/Operation
➢ Variable declarations
➢ Initialization: overtime payment to zero
➢ Constant definition: pension
➢ Print input prompt message
➢ Read corresponding input data
➢ Checking if the hours worked > 40 or not
➢ Calculate net salary by computing the following
✓ Pension (gross salary * 7%)
✓ Income tax (gross salary * income tax rate).
✓ Over-time payment (worked hours – 40 * bonus rate), if any
➢ Print output prompt message and the Net salary

Jan 2023
Solution
(Design the Program)
1. Variable declaration and initialization
➢ float gross_Salary, taxRate, bonusRate, overTime = 0.0;
➢ int hrsWorked
2. Constant definition
➢ const float penstionRate = 0.07;
3. Reading input data
➢ cout<<“Eneter gross salary, tax rate, hrs worked separated by space: “;
➢ cin>>gross_Salary>>taxRate>>bonusRate

Jan 2023
Solution
(Design the Program)
You can compile it
and make one
statement
4. Compute net Salary
➢ if (hrsWorked > 40) ➔ overtime = bonusRate * (hrsworked - 40 )
➢ gross_Salary += Overtime;
➢ float incomeTax = gross_Salary * taxRate;
➢ float penstion = gross_Salary * pensionRate;
➢ netSalary = gross_Salary – incomeTax – pesntion
5. Print result (net Salary)
➢ cout<< “The net Salary of the Employee is: “<<netSalary<<endl;

Jan 2023
Solution
–
Design
the
program

Jan 2023
I) if else Statement (two-selection)
▪ Syntax if (expression){
statement1 / block1
}else{
statement2 / block2;
}
next statement(s);

Jan 2023
Cont’d
Another Syntax ----- > without the block { }
➢ Can be used when there is only one statement
➢ Not suggested (it causes dangling Else
Problem)
if (condition)
<statement_true>;
else
<statement_false>;
if (condition)
<statement_true>;
When it can be used?
➢ It can be used when there are two different operations to be performed based on the pre-
defined condition.

Jan 2023
III) Conditional/Ternary operator
▪ It is an alternative selection
statement for the if …. else
statement
▪ Syntax
Condition ? Expr 1 : Expr 2;

Jan 2023
Exercise 4.2
Problem description
Write a C++ program to check whether a given integer number is (a) even/odd or
(b) positive or negative using the two-way selection statements;
➢ if ... else statement
Purpose: To demonstrate the use case of the two selection statements
Outcome: You able to identify and differentiate the various selection statements

Jan 2023
Solution
LET’S DO TOGETHER
➢ Perform an Analysis of the problem
➢ Design the program on paper
➢ Write the program.

Jan 2023
V) if .. else if Statement
Syntax
if (expression1){
statement1 / block1
}
else if (expression2){
statement2 / block2;
}
. . . . .
else {
statement-N / block-N;
}
next statement(s);
This selection statement allows
for conditional execution based
on more than two alternatives

Jan 2023
▪ if the condition (Boolean expression) is TRUE
(evaluated to 1), then statement1 or block1
that follows the selection is executed and
then the next statement(s) get executed.
▪ Otherwise block2 of each else if part is
evaluated and the statement2 or block2 of
the selection that returns TRUE is executed
and the execution continues with the next
statement in the program.
▪ If there is no condition evaluated to TRUE,
the else part will be executed.
Description
Cont’d

Jan 2023
Exercise 4.3
Problem description
1. Write a program to find the largest number of three numbers using if...else
statement
2. Write a program that reads a valid student mark score and prints the
corresponding GRADE scale as follows. [Hint: solve it using both nested if …. else and
if … else if statements)
3. Make a program that calculates and display the Body Mass Index (BMI) of a
person along with it’s status (normal, under-weight or over-weight.

Jan 2023
Cont. . . .
Purpose:
➢ To demonstrate the use case of the multiple selection statements
➢ To differentiate the use case of the nested two-way selection and multiple
selection statements
Outcome:
➢ You able to design and write a program with multiple execution alternatives
and determine the difference between the various selection statements.

Jan 2023
Summary
In this section, we briefly discussed and demonstrated;
➢ If statement
➢ If …. else statement
➢ If … else if statement

Jan 2023
(Nested if … else statement)

Jan 2023
Iv) Nested if … else statement
▪ Sometimes there is a situation
when one condition is based on the
other previous one.
▪ Nested statement refers to using
within another selection statement
▪ Match each else with the last
unmatched if

Jan 2023
Cont. . .
Example:
▪ A program used to determine if a given
symbol is a digit or upper case letter or
lower case letter.

Jan 2023
Exercise 4.4
Problem description
Write a C++ program that read a student mark score and print a message
“Congratulation!” for a score >= 50 otherwise “Failed, try harder!” using the two-way
selection statements;
➢ if ... else statement
➢ Nested if … else statement
Purpose: To demonstrate the use case of the two selection statements
Outcome: You able to identify and differentiate the various selection statements

Jan 2023
Summary
In this section, we briefly demonstrated;
➢ Nested if else if statement
➢ Solved practical exercise

Jan 2023
(switch statement)

Jan 2023
VI) Switch Statement Syntax
Switch statement is similar to if … else if
combination, it enables you to test several
cases generated by a given expression

Jan 2023
Cont. . .
➢ First the switch expression is evaluated once
➢ The value of the expression is compared with the values of each case
➢ If there is a match, the statements following the matched case (associated block )
will be executed until a break statement is reached.
➢ When a break statement is reached, the switch terminates, and the flow of
control jumps to the next line following the switch statement.
➢ A switch statement can have an optional default case (equivalent to else), which
usually appears at the end of the switch.
➢ The default case holds tasks to be executed when none of the cases is true.
How it works

Jan 2023
Cont. . .
➢ The expression must be evaluated to literal value (integral or character or Boolean
or enum) and can only be used to compare an expression against constants
➢ Each case is followed by the value to be compared to and a colon.
➢ The expression of each case statement in the block must be unique and cannot be
either a variable or range.
➢ If no break appears, the flow of control will fall through to subsequent cases until a
break is reached.
➢ It is not necessary to include block - braces {} surrounding the statements of the cases
➢ Even if it is usually necessary to include a break statement at the end of each case,
there are situations in which it makes sense to have a case without a break.
Important Note

Jan 2023
Exercise 4.5
Problem description
Write a basic calculator program that reads an operator and numbers from the
user and prints the result. [Hint: switch-case statement)
Purpose:
✓ To demonstrate the use case of the
switch-case statements
Outcome:
✓ You able to write a menu-based
program using switch-case statements
Solution [LET’S DO TOGETHER]
➢ Perform an Analysis of the problem
➢ Design the program on paper
➢ Write the program.

Jan 2023
Case Evaluation
Which selection statement is the best fit for this problem (has range selection)?

Jan 2023
Dangling else problem
Output
✓ It displays the “4 is an odd
number” message
Case study
➢ What does it display for x=4?

Jan 2023
Cont. . .
Problem
✓ 4 is a positive even numbers
✓ Reason is that else belongs to the most recent if
✓ The indentation says the reverse, else belongs to second (inner) if
Solution:
✓ using brace {}

Jan 2023
Short-circuit Evaluation
✓ Short-circuit evaluation refers to the order of Boolean expression evaluation in the
selection statement
✓ During the selection evaluation, the first (leftmost) Boolean sub-expression is
evaluated.
✓ If its value is enough to judge the value of the entire expression, then stop there.
Otherwise, continue evaluation towards the right.
✓ Example: if (count != 0 && scores/count < 60) cout<<"low average";
▪ In this example, if the value of count is zero, then first sub-expression becomes
false and the second one is not evaluated.
▪ In this way, we avoid “division by zero” error (that would cause to stop the
execution of the program)
✓ Alternative method without using short-circuit evaluation is using nested statement

Jan 2023
Summary
In this section, we briefly discussed and demonstrated;
➢ Switch statement
➢ Switch statement Vs. If else if statement
➢ Dangling else problem
➢ Short-circuit Evaluation

Jan 2023
Problems Solving and
Practical Exercises
(Refer worksheet 3)

Jan 2023
Reading Resources/Materials
eBooks
▪ Chapter 5 & 6: Diane Zak; An Introduction to Programming with C++ [8th Edition],
2016 Cengage Learning
▪ Chapter 4: Gary J. Bronson; C++ For Engineers and Scientists [3rd edition],
Course Technology, Cengage Learning, 2010
▪ Chapter 2 (section 2.4): Walter Savitch; Problem Solving With C++ [10th edition],
University of California, San Diego, 2018
▪ Chapter 4: P. Deitel , H. Deitel; C++ how to program, [10th, Global Edition] (2017)

Jan 2023
eBooks – looping statements
▪ Chapter 7 & 8: Diane Zak; An Introduction to Programming with C++ [8th Edition],
2016 Cengage Learning
▪ Chapter 5: Gary J. Bronson; C++ For Engineers and Scientists [3rd edition],
Course Technology, Cengage Learning, 2010
▪ Chapter 2 (section 2.4): Walter Savitch; Problem Solving With C++ [10th edition],
University of California, San Diego, 2018
▪ Chapter 4 & 5: P. Deitel , H. Deitel; C++ how to program, [10th, Global Ed.] (2017)

Jan 2023
Online Materials
▪ https://www.w3schools.com/cpp/default.asp
▪ https://www.javatpoint.com/cpp-tutorial
▪ https://www.programiz.com/cpp-programming
▪ https://www.hackerrank.com/domains/cpp
▪ https://cplusplus.com/doc/tutorial/

Jan 2023
Thank You
For Your Attention!!

Fundamentals of Computer Programming - Flow of Control I

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