Lesson 9.1 value returning

© 2016 Cengage Learning®. May not be scanned, copied or
Introduction to Programming in C++
Eighth Edition
Lesson 9.1:
Value-Returning Functions
duplicated, or posted to a publicly accessible website, in whole
or in part.

• Raiseanumber to apower using the pow function
• Return the square root of anumber using thesqrt
function
• Generate random numbers
• Create and invoke afunction that returns avalue
• Passinformation by value to afunction
• Write afunction prototype
• Understand avariable’s scope and lifetime
or in part.
2An Introduction to Programming with C++, Eighth Edition
Objectives

• Afunction is ablock of code that performs atask
• Every C++program contains at least one function
(main)
– Most contain manyfunctions
• Somefunctions are built-in functions (part ofC++):
defined in languagelibraries
• Others, called program-defined functions, arewritten
by programmers; defined in aprogram
• Functions allow for blocks of code to be used many
times in aprogram without having toduplicate code
or in part.
Functions

• Functions also allow large, complex programs to be
broken down into small, manageablesub-tasks
• Eachsub-task is solved by afunction, and thus different
people can write different functions
• Many functions can then be combined intoasingle
program
• Typically, main is used to call other functions, but any
function can call any other function
or in part.
Functions (cont’d.)

Figure 9-1 Illustrations of value-returning and void functions
or in part.

• All functions are either value-returning orvoid
• All value-returning functions perform atask and then
return precisely onevalue
• In most cases,the value is returned to the statement
that called thefunction
• Typically, astatement that calls afunction assignsthe
return value to avariable
– However, areturn value could also be usedin a
comparison or calculation or could be printed to the
screen
or in part.
Value-Returning Functions

• Thepow function is aconvenient tool to raise anumber
to apower (exponentiation)
• Thepow function raises anumber to apower and
returns the result asadouble number
• Syntax is pow(x, y), in which x is the base and y is the
exponent
• At least one of the twoarguments must be adouble
• Program must contain the #include <cmath>
directive to usethe powfunction
or in part.
The pow Function

Figure 9-2 How to use the pow function
The pow Function (cont’d.)
or in part.

• sqrt function is abuilt-in value-returning function that
returns anumber’s square root asadouble
• Definition contained in cmathlibrary
–Program must contain #include <cmath>to useit
• Syntax: sqrt(x), in which x is a double or float
–Here, xis an actualargument, which is an item of
information afunction needs toperform its task
• Actual arguments are passed to afunction whencalled
or in part.
The sqrt Function

Figure 9-3 How to use the sqrt function
The sqrt Function (cont’d.)
or in part.

• Program that calculates and displays the length ofa
right triangle hypotenuse
• Program usesPythagorean theorem
– Requires squaring and taking squareroot
• powfunction can be used to square
• sqrtfunction can be used to take square root
• Both are built-in value-returning functions
or in part.
The Hypotenuse Program

Figure 9-4 Pythagorean theorem
The Hypotenuse Program (cont’d.)
or in part.

Figure 9-5 Problem specification, IPO chart information, and C++
instructions for the Hypotenuse Program
or in part.

Figure 9-6 Beginning of Hypotenuse program
or in part.

Figure 9-6 Completion of Hypotenuse Program and sample run
or in part.

• C++provides apseudo-random numbergenerator
– Producesasequence of numbers that meetcertain
statistical requirements forrandomness
– Numbers chosen uniformly from finite set of numbers
– Not truly random but sufficient for practical purposes
• Random number generator in C++:rand function
–Returns an integer between 0 and RAND_MAX, inclusive
– RAND_MAX is abuilt-in constant (>= 32767)
or in part.
The rand, srand, and time
Functions

• rand function’s syntax: rand()
– Doesn’t require any actual arguments, but parenthesesare
still required
• Expression:
lowerBound + rand() % (upperBound – lowerBound + 1)
– Allows ranges other than 0 to RAND_MAX to be used
– Rangeis upperBound to lowerBound
• Initialize random number generator eachtime
– Otherwise, will produce the samesequence
or in part.

Figure 9-7 How to use the rand function
or in part.

Figure 9-8 How to generate random integers within a specific range
or in part.

• Use srand function (a void function) to initialize
random number generator
• Syntax: srand(seed), in which seed is an integer
actual argument that represents the starting point of
the generator
–Commonly initialized using the time function
• Ensuresunique sequence of numbers for eachprogram
run
or in part.

• time function is a value-returning function that
returns current time in number of seconds since
January 1, 1970
– Returns a time_t object, so must be cast to an integer
before passingto srand
– Program must contain #include <ctime> directive
to useit
or in part.

Figure 9-9 How to use the srand function
or in part.

Lesson 9.1 value returning

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Lesson 9.1 value returning