Chapter 02 - Problem Solving

Introduction to Programming in C++
Seventh Edition
Chapter 2:
Beginning the Problem-Solving Process

• Explain the problem-solving process used to create a
computer program
• Analyze a problem
• Complete an IPO chart
• Plan an algorithm using pseudocode and flowcharts
• Desk-check an algorithm
Chapter Objectives
2An Introduction to Programming with C++, Seventh Edition

• People solve hundreds of simple problems every day
without thinking about how they do it
• Understanding the thought process involved can help in
solving more complex problems
• You can also use a similar process to design a computer
solution to a problem (computer program)
Problem Solving

• First step in solving a problem: analyze it
– Example: paying and mailing a bill
• Next, you plan, review, implement, and evaluate the
solution
• After this, it may be necessary to modify the solution
Solving Everyday Problems

Solving Everyday Problems (cont’d.)
Figure 2-1 Summary of the analysis and planning steps for
the bill paying problem

Solving Everyday Problems (cont’d.)
Figure 2-2 Modified algorithm for the bill paying problem

• A similar process to everyday problem solving is used to
create computer programs
• A computer program is a solution implemented on a
computer
• There are six steps to creating a computer solution to a
problem
Creating Computer Solutions to Problems

Creating Computer Solutions to Problems
(cont’d.)
Figure 2-3 How to create a computer solution to a problem

• It is essential to understand a problem before creating a
solution to it
• Analyze a problem to:
– Determine the goal of solving it (Output)
– Determine the items needed to achieve that goal (Input)
• Always search first for the output
Step 1−Analyzing the Problem

Step 1−Analyzing the Problem (cont’d.)
Figure 2-4 Problem specification for Treyson Mobley

• Some programmers use an IPO chart to organize and
summarize the results of a problem analysis
– IPO: Input, processing, and output
Step 1−Analyzing the Problem (cont’d.)
Figure 2-5 Partially completed IPO chart
showing the input and output items

• Several readings of the problem may be necessary to
fully understand the problem
• Cross out irrelevant information in the problem
description
Hints for Analyzing Problems
Figure 2-6 Problem specification with
unimportant information crossed out

• Some problem specifications contain incomplete
information
Hints for Analyzing Problems (cont’d.)
Figure 2-7 Problem specification that does
not contain enough information

• Distinguish between information that is missing and
information that is implied
Hints for Analyzing Problems (cont’d.)
Figure 2-8 Problem specification in
which the input is not explicitly stated

• Algorithm: set of instructions that will transform the
problem’s input into its output
– Record in the Processing column of the IPO chart
– Can be written as pseudocode or a flowchart
• Pseudocode: tool programmers use to help plan an
algorithm
– Short English statements
– Not standardized
– Not understandable by a computer
Step 2−Planning the Algorithm

Step 2−Planning the Algorithm (cont’d.)
Figure 2-9 Problem specification and IPO
chart for the Treyson Mobley problem

• Flowcharts are also used to plan an algorithm
– Use standardized symbols
– Symbols connected with flowlines
– Oval: start/stop symbol
• Represents beginning and end of algorithm
– Rectangle: process symbol
• Represents tasks such as calculations
– Parallelogram: input/output symbol
• Represents I/O tasks

Figure 2-10 Figure 2-9’s algorithm in flowchart form

• A problem can have more than one solution
Figure 2-11 A different solution to the
Treyson Mobley problem (pseudocode)

• Processing item: an intermediate
value (neither input nor output)
the algorithm uses to transform
input into output
Figure 2-11 A different solution to the
Treyson Mobley problem (flowchart)

Step 3−Desk-Checking the Algorithm
• Desk-checking an algorithm verifies that it is correct
– Refers to checking an algorithm by hand, rather than
with a computer
– Also called hand-tracing
• Choose sample data and manually compute the expected
output value
• Creating a desk-check table can be helpful

(cont’d.)
Figure 2-12 Manual tip calculation for the first desk-check

(cont’d.)
Figure 2-13 Treyson Mobley solution and
partially completed desk-check table

(cont’d.)
Figure 2-14 Input values entered in the desk-check table
Figure 2-15 Processing item’s value
entered in the desk-check table
Figure 2-16 Output value entered in the desk-check table

(cont’d.)
Figure 2-17 Manual tip calculation for
the second desk-check

Figure 2-19 Value of the second desk-check’s
processing item entered in the desk-check table
Figure 2-20 Value of the second desk-check’s
output item entered in the desk-check table
Figure 2-18 Second set of input values
entered in the desk-check table
(cont’d.)

• Valid data: data that the algorithm is expecting the user
to enter
• Invalid data: data that the algorithm is not expecting
the user to enter
• You should test an algorithm with invalid data
– Users may make mistakes when entering data
(cont’d.)

The Gas Mileage Problem
Figure 2-21 Problem specification for the gas mileage problem

The Gas Mileage Problem (cont’d.)
• Plan the algorithm with an IPO chart
Figure 2-22 IPO chart for the gas mileage problem

• Then desk-check the algorithm
The Gas Mileage Problem (cont’d.)
Figure 2-23 Desk-check table for the gas mileage problem

• Problem solving typically involves analyzing the
problem and then planning, reviewing, implementing,
evaluating, and modifying (if necessary) the solution
• Programmers use tools (IPO charts, pseudocode,
flowcharts) to help them analyze problems and develop
algorithms
• The first step in problem solving is to analyze the
problem
– First determine the output and then the input
Summary

• The second step is to plan the algorithm
– Write the steps that will transform the input into the
output
– Most algorithms begin with entering input data, then
processing the data, then displaying the output
• The third step is to desk-check the algorithm
– Choose sample data and manually compute the expected
output
– Create a desk-check table to fill in values step by step
Summary (cont’d.)

• Aiden Nelinski is paid every Friday and will receive
either a 2.0% or 2.5% raise next week
• He wants a program that calculates and displays the
amount of his new weekly pay
Lab 2-1: Stop and Analyze
Figure 2-26 IPO chart for Lab 2-1

• Create an algorithm for the manager of the Lakeview
Hotel
Lab 2-2: Plan and Create
Figure 2-30 Completed IPO chart for Lab 2-2

• Each guest of the Lakeview Hotel pays an
entertainment tax, which is a percentage of the room
charge only
• Modify the IPO chart in Figure 2-30
• Desk-check the algorithm twice using the given values
Lab 2-3: Modify

• An algorithm is given to calculate and display an annual
property tax
• Desk-check the algorithm three times using the given
values
Lab 2-4: Desk-Check

• An algorithm is given to calculate and display the
average of three numbers but is incorrect
• Find and correct the errors in the algorithm
Lab 2-5: Debug
Figure 2-42 Corrected algorithm for Lab 2-5

Chapter 02 - Problem Solving

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Chapter 02 - Problem Solving