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Programming
Fundamentals
By
Adnan Waheed
University of Narowal
Control Structure
(Selection Statements)
Lecture No. 12
Tuesday, November 21, 2023

Avoiding Bugs by Avoiding Partially
Understood Concepts and
Techniques
• Must use concepts and techniques
correctly;
– Otherwise solution will be either incorrect or
deficient
• If you do not understand a concept or
technique completely
– Don’t use it
– Save yourself an enormous amount of
debugging time
C++ Programming: Program Design Including Data Structures, Fifth Edition 2

Input Failure and the if
Statement
• If input stream enters a fail state
– All subsequent input statements associated
with that stream are ignored
– Program continues to execute
– May produce erroneous results
• Can use if statements to check status of
input stream
• If stream enters the fail state, include
instructions that stop program execution

Confusion Between the Equality
(==) and Assignment (=) Operators
• C++ allows you to use any expression that
can be evaluated to either true or false
as an expression in the if statement:
if (x = 5)
cout << "The value is five." << endl;
• The appearance of = in place of ==
resembles a silent killer
– It is not a syntax error
– It is a logical error

Program Style and Form
(Revisited): Indentation
• If your program is properly indented
– Spot and fix errors quickly
– Show the natural grouping of statements
• Insert a blank line between statements that
are naturally separate
• Two commonly used styles for placing braces
– On a line by themselves
– Or left brace is placed after the expression, and
the right brace is on a line by itself

Using Pseudocode to Develop,
Test, and Debug a Program
• Pseudocode, or just pseudo
– Informal mixture of C++ and ordinary
language
– Helps you quickly develop the correct
structure of the program and avoid making
common errors
• Use a wide range of values in a walk-
through to evaluate the program

switch Structures
• switch structure:
alternate to if-else
• switch (integral)
expression is evaluated
first
• Value of the expression
determines which
corresponding action is
taken
• Expression is sometimes
called the selector

switch Structures
• Syntax
switch(expression) {
case x:
// code block
break;
case y:
// code block
break;
default:
// code block
•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
associated block of code is
executed
•The break and default keywords
are optional

switch Structures (cont'd.)

Switch Example
• The example below uses the weekday number to calculate the weekday
name:
int day = 4;
switch (day) {
case 1:
cout << "Monday";
break;
case 2:
cout << "Tuesday";
break;
case 3:
cout << "Wednesday";
break;
case 4:
cout << "Thursday";
break;
case 5:
cout << "Friday";
break;
case 6:
cout << "Saturday";
break;
case 7:
cout << "Sunday";
break; // Outputs "Thursday" (day 4)

The break Keyword
• When C++ reaches a break keyword, it breaks out of the switch
block.
• This will stop the execution of more code and case testing inside
the block.
• When a match is found, and the job is done, it's time for a break.
There is no need for more testing.

The default Keyword
The default keyword specifies some code to run if there is no case match:
int day = 4;
switch (day) {
case 6:
cout << "Today is Saturday";
break;
case 7:
cout << "Today is Sunday";
break;
default:
cout << "Looking forward to the Weekend";
}
// Outputs "Looking forward to the Weekend.

switch Structures (cont'd.)

Output = ?

Avoiding Bugs by Avoiding Partially
Understood Concepts and
Techniques: Revisited
• To output results correctly
– The switch structure must include a break
statement after each cout statement

COMPLETE EXAMPLE @
HOME FOR PRACTICE OF
STUDENTS

Programming Example: Cable
Company Billing
• This programming example calculates a
customer’s bill for a local cable company
• There are two types of customers:
– Residential
– Business
• Two rates for calculating a cable bill:
– One for residential customers
– One for business customers

Programming Example: Rates
• For residential customer:
– Bill processing fee: $4.50
– Basic service fee: $20.50
– Premium channel: $7.50 per channel
• For business customer:
– Bill processing fee: $15.00
– Basic service fee: $75.00 for first 10
connections/$5.00 for each additional one
– Premium channel cost: $50.00 per channel for
any number of connections

Programming Example:
Requirements
• Ask user for account number and
customer code
• Assume R or r stands for residential
customer and B or b stands for business
customer

Programming Example: Input and
Output
• Input:
– Customer account number
– Customer code
– Number of premium channels
– For business customers, number of basic
service connections
• Output:
– Customer’s account number
– Billing amount

Programming Example: Program
Analysis
• Purpose: calculate and print billing amount
• Calculating billing amount requires:
– Customer for whom the billing amount is
calculated (residential or business)
– Number of premium channels to which the
customer subscribes
• For a business customer, you need:
– Number of basic service connections
– Number of premium channels

Programming Example: Program
Analysis (cont'd.)
• Data needed to calculate the bill, such as
bill processing fees and the cost of a
premium channel, are known quantities
• The program should print the billing
amount to two decimal places

Programming Example: Algorithm
Design
• Set precision to two decimal places
• Prompt user for account number and
customer type
• If customer type is R or r
– Prompt user for number of premium channels
– Compute and print the bill
• If customer type is B or b
– Prompt user for number of basic service
connections and number of premium channels
– Compute and print the bill

Programming Example: Variables
and Named Constants

Programming Example:
Formulas
Billing for residential customers:
amountDue = RES_BILL_PROC_FEES +
RES_BASIC_SERV_COST
+ numOfPremChannels *
RES_COST_PREM_CHANNEL;

Programming Example: Formulas
(cont'd.)
Billing for business customers:
if (numOfBasicServConn <= 10)
amountDue = BUS_BILL_PROC_FEES +
BUS_BASIC_SERV_COST
BUS_COST_PREM_CHANNEL;
else
amountDue = BUS_BILL_PROC_FEES +
BUS_BASIC_SERV_COST
+ (numOfBasicServConn - 10)
* BUS_BASIC_CONN_COST
BUS_COST_PREM_CHANNEL;

Programming Example: Main
Algorithm
1. Output floating-point numbers in fixed
decimal with decimal point and trailing zeros
– Output floating-point numbers with two decimal
places and set the precision to two decimal
places
2. Prompt user to enter account number
3. Get customer account number
4. Prompt user to enter customer code
5. Get customer code

Algorithm (cont'd.)
6. If the customer code is r or R,
– Prompt user to enter number of premium
channels
– Get the number of premium channels
– Calculate the billing amount
– Print account number and billing amount

Algorithm (cont'd.)
7. If customer code is b or B,
– Prompt user to enter number of basic
service connections
– Get number of basic service connections
– Prompt user to enter number of premium
channels
– Get number of premium channels
– Calculate billing amount
– Print account number and billing amount

Algorithm (cont'd.)
8. If customer code is other than r, R, b,
or B, output an error message

Summary
• Control structures alter normal control flow
• Most common control structures are
selection and repetition
• Relational operators: ==, <, <=, >, >=, !=
• Logical expressions evaluate to 1 (true)
or 0 (false)
• Logical operators: ! (not), && (and), ||
(or)

Summary (cont'd.)
• Two selection structures: one-way selection
and two-way selection
• The expression in an if or if...else
structure is usually a logical expression
• No stand-alone else statement in C++
– Every else has a related if
• A sequence of statements enclosed between
braces, { and }, is called a compound
statement or block of statements

Summary (cont'd.)
• Using assignment in place of the equality
operator creates a semantic error
• switch structure handles multiway
selection
• break statement ends switch statement
• Use assert to terminate a program if
certain conditions are not met

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UoN-Lec_12_Control_Structure.pdf

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