The document discusses using counters and accumulators to solve problems that require calculating a total or average. It provides examples of initializing counters and accumulators to 0 and updating them by adding a constant value (for counters) or varying value (for accumulators) in a loop. A sample stock price program is presented that uses a counter to track the number of prices entered and an accumulator to track the total, then calculates the average. Counter-controlled loops are also discussed as another method of controlling loops.

1. © 2016 Cengage Learning®. May not be scanned, copied or
Introduction to Programming in C++
Eighth Edition
Lesson 7.2:
Using Counters and Accumulators
duplicated, or posted to a publicly accessible website, in whole
or in part.

2. • Someproblems require you to calculate atotal or
average
• Todo this, you use acounter, accumulator, or both
• Acounter is anumeric variable used for counting
something
• An accumulator is anumeric variable used for
accumulating (adding together) multiple values
• Two tasks are associated with counters and
accumulators: initializing andupdating
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
2An Introduction to Programming with C++, Eighth Edition
Using Counters and Accumulators

3. • Initializing means assigningabeginning value to a
counter or accumulator (usually 0) – happensonce,
before the loop isprocessed
• Updating (or incrementing) means adding anumber to
the value of acounter oraccumulator
• Acounter is updated by aconstant value (usually1)
• An accumulator is updated by avalue that varies
• Update statements are placed in the body ofaloop
since they must be performed at eachiteration
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
3An Introduction to Programming with C++, Eighth Edition
Using Counters and Accumulators
(cont’d.)

4. Using Counters and Accumulators
(cont’d.)
Figure 7-13 Example of a partial game program that uses a counter
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
4An Introduction to Programming with C++, Eighth Edition

5. Using Counters and Accumulators
(cont’d.)
Figure 7-14 Syntax and examples of update statements for counters
and accumulators
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
5An Introduction to Programming with C++, Eighth Edition

6. • Example problem and program solution (following
slides)
– Program takes in asequence of stock prices fromthe
keyboard and outputs theiraverage
– Usesacounter to keep track of the number of prices
entered and an accumulator to keep track of the total
– Both are initialized to 0
– Theloop endswhen the user enters asentinel value(-1)
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
6An Introduction to Programming with C++, Eighth Edition
The Stock Price Program

7. The Stock Price Program (cont’d.)
Figure 7-15 Problem specification for the Sales Express program
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
7An Introduction to Programming with C++, Eighth Edition

8. Figure 7-15 IPO chart information and C++ instructions for
the Stock Price program
The Stock Price Program (cont’d.)
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
8An Introduction to Programming with C++, Eighth Edition

9. The Stock Price Program (cont’d.)
Figure 7-16 Flowchart for the Stock Price program
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
9An Introduction to Programming with C++, Eighth Edition

10. The Stock Price Program (cont’d.)
Figure 7-17 Desk-check table after the first update to the counter
and accumulator variables
Figure 7-18 Desk-check table after the second update to the
counter and accumulator variables
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
10An Introduction to Programming with C++, Eighth Edition

11. The Stock Price Program (cont’d.)
Figure 7-19 Completed desk-check table and sample runs for the
Stock Price program
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duplicated, or posted to a publicly accessible website, in whole
or in part.
11An Introduction to Programming with C++, Eighth Edition

12. • Loopscan be controlled using acounter rather thana
sentinel value
• Theseare called counter-controlled loops
• Example problem and program solution (following
slides)
– Counter-controlled loop is used thattotals the quarterly
salesfrom three regions
– Looprepeats three times, once for eachregion, usinga
counter to keeptrack
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
12An Introduction to Programming with C++, Eighth Edition
Counter-Controlled Pretest Loops

13. Counter-Controlled Pretest Loops
(cont’d.)
Figure 7-20 Problem specification, IPO chart information, and C++
instructions for the modified Stock Price program
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
13An Introduction to Programming with C++, Eighth Edition

14. Counter-Controlled Pretest Loops
(cont’d.)
Figure 7-20 Problem specification, IPO chart information, and C++
instructions for the modified Stock Price program (cont’d.)
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
14An Introduction to Programming with C++, Eighth Edition

15. Figure 7-21 Flowchart for the modified Stock Price program
Counter-Controlled Pretest Loops
(cont’d.)
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
15An Introduction to Programming with C++, Eighth Edition

16. Figure 7-22 Completed desk-check table and sample run for the
modified Stock Price program
Counter-Controlled Pretest Loops
(cont’d.)
© 2016 Cengage Learning®. May not be scanned, copied or
duplicated, or posted to a publicly accessible website, in whole
or in part.
16An Introduction to Programming with C++, Eighth Edition