Lesson 9.2 guessing the game program

© 2016 Cengage Learning®. May not be scanned, copied or
Introduction to Programming in C++
Eighth Edition
Lesson 9.2:
Guessing the Game Program
duplicated, or posted to a publicly accessible website, in whole
or in part.

• Program generates arandom number from 1 to 10and
then allows the user asmany choices asneeded to
guessthe number.
• Thesrand, time, and randfunctions are all utilized
in the program.
or in part.
2An Introduction to Programming with C++, Eighth Edition
The Guessing Game Program

The Guessing Game Program(cont’d.)
Figure 9-10 Problem specification, IPO chart information, and C++
instructions for the Guessing Game Program
or in part.

The Guessing Game Program(cont’d.)
Figure 9-11 Guessing Game Program and sample run
or in part.

• Aprogram-defined value-returning function definition
is composed of aheader and abody
• Header (first line) contains return data type,name of
function, and an optional parameterList
– Rules for function namesare sameasfor variables
– Goodidea to usemeaningful namesthat describe
function’s purpose
– Memory locations in parameterList are calledformal
parameters
• Eachstores an item of information passedtothe function
when it iscalled
or in part.
Creating Program-Defined Value-
Returning Functions

• Function body contains instructions for performingthe
function’s assigned task
• Surrounded by braces({})
• Laststatement is usually the return statement
– Returns one value (must match return data typein
function header)
• After returnstatement is processed, program
execution continues in callingfunction
• Good idea to include comment (such as//end of
functionName) to mark end offunction
or in part.
Returning Functions (cont’d.)

Figure 9-12 How to create a program-defined value-returning function
Returning Functions (cont’d.)
or in part.

Figure 9-12 How to create a program-defined value-returning function
Creating Program-Defined Value-Returning
Functions (cont’d.)
or in part.

• Afunction must be called (invoked) to perform itstask
• mainis automatically called when program is run
• Other functions must be called by astatement
• Syntax for calling afunction:
functionName([argumentList]);
– argumentList is list of actual arguments (ifany)
– Anactual argument canbe avariable, named constant,
literal constant, orkeyword
or in part.
Calling a Function

• Value-returning functions are typically calledfrom
statements that:
– Assignthe return value to avariable
– Usethe return value in acalculation orcomparison
– Display the return value
• Acall to avoid function is an independent statement
because void functions do not returnvalues
or in part.
Calling a Function (cont’d.)

• C++allows you to passeither avariable’s value or its
addressto afunction
• Passingavariable’s value is referred to aspassingbyvalue
• Passingavariable’s address is referred to aspassingby
reference
• Default is passing by value
• Number, data type, and ordering ofactual arguments must
match the formal parameters in functionheader
– Namesdo not need to match (differentnamesare better)
or in part.

Figure 9-13 How to call (invoke) a value-returning function
or in part.

Figure 9-14 Function call and function definition
or in part.

• Theprogram allows the user to enter the initial deposit
made into asavings account and the annual interest rate.
• Theprogram displays the amount of money in the
account at the end of1 through 3 years, assumingno
additional deposits or withdrawals aremade.
or in part.
The Savings Account Program

(cont’d.)
Figure 9-15 Problem specification, IPO chart information,
and C++ instructions for the Savings Account Program
© 2016 Cengage Learning®. May not be scanned, copied or 15An Introduction to Programming with C++, Eighth Edition duplicated, or posted to a publicly accessible website, in whole
or in part.

(cont’d.)
Figure 9-15 Problem specification, IPO chart information,
and C++ instructions for the Savings Account Program
© 2016 Cengage Learning®. May not be scanned, copied or 16An Introduction to Programming with C++, Eighth Edition duplicated, or posted to a publicly accessible website, in whole
or in part.

Figure 9-16 Flowcharts for the Savings Account Program
(cont’d.)
or in part.
An Introduction to Programming with C++, Eighth Edition 17

• When afunction definition appears below the main
function, you must enter afunction prototypeabove the
main function
• Afunction prototype is astatement that specifies the
function’s name, data type of its return value, and data
type of each of its formal parameters (if any)
– Namesfor the formal parameters are notrequired
• Programmers usually place function prototypes at
beginning of program, after the #includedirectives
or in part.
Function Prototypes

Figure 9-17 How to write a function prototype
Function Prototypes (cont’d.)
or in part.

Figure 9-18 Savings Account Program
Completing the Savings Account
Program
or in part.

• Avariable’s scope indicates where in the programthe
variable can be used
• Avariable’s lifetime indicates how long the variable
remains in the computer’s internalmemory
• Both scope and lifetime are determined by whereyou
declare the variable in theprogram
• Variables declared within afunction and those that
appear in afunction’s parameterList have alocal scope
and are referred to aslocalvariables
or in part.
The Scope and Lifetime of a Variable

• Localvariables can be used only by the function inwhich
they are declared or in whose parameterList theyappear
– Remainin internal memory until the function ends
• Global variables are declared outside of any functionin
the program
– Remainin memory until the programends
• Any statement can useaglobal variable
or in part.
(cont’d.)

• Declaring a variable as global can allow unintentional
errors to occur
– e.g., a function that should not have access to the variable
inadvertently changesthe variable’s contents
• Youshould avoid using global variables unless necessary
• If more than one function needs to accessthe same
variable, it is better to create a local variable in one
function and pass it to other functions that need it
or in part.
(cont’d.)

Lesson 9.2 guessing the game program

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Lesson 9.2 guessing the game program