C++ Programming: Program Design Including Data Structures, Fourth Edition
Chapter 6
User-Defined Functions I
At a Glance
Instructor’s Manual Table of Contents

Overview

Objectives

Teaching Tips

Quick Quizzes

Class Discussion Topics

Additional Projects

Additional Resources

Key Terms
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C++ Programming: Program Design Including Data Structures, Fourth Edition
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Lecture Notes
Overview
Chapter 6 focuses on functions. First, students will learn more about the predefined
functions in C++. Then they will learn about the use of user-defined functions to break a
program into manageable pieces. Students will examine the mechanics of writing their
own functions, including how to use parameters and return values. By the end of the
chapter, students will be able to construct programs using both predefined and userdefined functions.
Objectives
In this chapter, the student will:
 Learn about standard (predefined) functions and discover how to use them in a program
 Learn about user-defined functions
 Examine value-returning functions, including actual and formal parameters
 Explore how to construct and use a value-returning, user-defined function in a program
Teaching Tips
Predefined Functions
1. Compare C++ predefined functions to algebraic functions. Use the functions in the
cmath library to illustrate the concept of a function as it relates to programming.
2. Review some of the C++ header files and predefined functions listed in Table 6-1.
3. Illustrate the use of C++ predefined functions using Example 6-1.
Teaching
Tip
Although your students have used C++ functions in previous chapters,
organizing their own programs into functions may be a new concept to them. Use
the predefined functions presented in this section to introduce the concept of
encapsulation. Emphasize the “black box” nature of a function. Explain that
although we need to know how to call a C++ function, we do not need to know
anything about its implementation. When we write our own functions, we will
call them in a similar fashion, although we may be aware of the implementation
of the function.
C++ Programming: Program Design Including Data Structures, Fourth Edition
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Quick Quiz 1
1. How many parameters does the C++ predefined function pow have?
Answer: two
2. The C++ function sqrt is of type ____________________.
Answer: double
3. To use predefined functions in a program, you must include the
____________________ that includes the function specification.
Answer: header file
4. The C++ function toupper returns a(n) ____________________ value.
Answer: int
User-Defined Functions
Teaching
Tip
Before introducing user-defined functions, spend some time discussing why the
use of functions is beneficial to a program. After all, the entire code of a program
could be written in the main function. Explain that functions enhance a
program’s readability, improve the development process by isolating code, and
allow several people to work on different portions of a program.
Teaching
Tip
This is also a good opportunity to visit the concept of reusability. Emphasize that
functions allow programmers to write code once and then reuse it as necessary.
The C++ predefined functions are an example of this concept.
1. Describe the two categories of user-defined functions in C++: value-returning functions
and void functions.
Value-Returning Functions
1. Briefly describe the items a programmer needs to know when using a predefined
function, including the header file name, the function name, the parameter type, and the
return type.
2. Discuss how the return value of a function is used in a program.
C++ Programming: Program Design Including Data Structures, Fourth Edition
Teaching
Tip
6-4
Use code snippets from the text to demonstrate how a function call can be used
in both an assignment statement and an output statement.
3. Define the terms function header, function body, and function definition. Use code
examples to describe the elements of a function.
4. Define the terms actual parameter and formal parameter and explain the difference
between the two.
Teaching
Tip
Spend some extra time discussing actual and formal parameters. These terms are
often used incorrectly or interchangeably. Verify that students understand that
formal parameters are placed in a function header as a definition, somewhat like
placeholders. Actual parameters are used when a program passes required values
to a function during a function call.
Syntax: Value-Returning Function
1. Explain the syntax of a value-returning function.
Teaching
Tip
Emphasize that a value-returning function only includes the data type of the
value that the function returns in the function header, not a return type and
identifier as in the parameter list.
Syntax: Formal Parameter List
1. Describe the syntax of a formal parameter list.
Teaching
Tip
Understanding how functions work is critical to successful programming, so it
might be wise to revisit basic function concepts throughout this chapter. In this
case, reiterate that parameter lists are used because functions often need input
values. Provide an example from the text.
Function Call
1. Briefly note the syntax used to call a function.
Syntax: Actual Parameter List
1. Step through the syntax of an actual parameter list.
C++ Programming: Program Design Including Data Structures, Fourth Edition
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2. Discuss the rules involving actual parameter lists, including matching data types and a
one-to-one correspondence with the formal parameter list. Note that the parameter list
can be empty, but the function call will still require parentheses after the function name.
Teaching
Tip
Briefly relate the actual parameter list syntax to the function call syntax to make
sure students understand how to write a complete function call expression. Also,
compare an actual function call with the corresponding function header to
demonstrate the one-to-one correspondence and matching data types of the
parameters.
Quick Quiz 2
1. A value-returning function is used (called) in a(n) ____________________.
Answer: expression
2. True or False: Void functions do not have a return type.
Answer: True
3. The code required to accomplish a function’s task is called the ____________________
of the function.
Answer: body
4. True or False: An actual parameter is a variable declared in the function heading.
Answer: False
return Statement
1. Explain the purpose of the return statement in a function.
Syntax: return Statement
1. Note the syntax of the return statement and describe its execution in detail.
2. Use the examples in this section to discuss different approaches of returning a value
from a function.
Teaching
Tip
Call attention to the compareThree function in this section to demonstrate
how a function can be used as a parameter. Note that this functionality is often
used in programming.
C++ Programming: Program Design Including Data Structures, Fourth Edition
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Function Prototype
1. Define the term function prototype and explain how it is used in C++ programs to avoid
compilation errors.
Syntax: Function Prototype
1. Step through the syntax of a function prototype. Emphasize the syntactic differences
between a function prototype and a function header.
2. Discuss the examples in the “Notes” at the end of this section to reiterate that a valuereturning function must return a value, and the data type of the value must match the
function type.
Palindrome Number (Example 6-4)
1. Discuss the Palindrome program and the function isNumPalindrome in particular.
Note that this function returns a bool value.
Flow of Execution
1. Describe in detail the flow of execution in a program with functions. Review the use of
function prototypes to facilitate compilation. Also, explain how a function call operates
during program execution.
2. Step through the “Largest Number” and “Cable Company” Programming Examples to
consolidate the concepts presented in this chapter. Encourage students to compile and
run these programs on their own.
Quick Quiz 3
1. What is a local declaration?
Answer: A declaration of a variable inside a function for use only within that function
2. True or False: When a return statement executes in a function, the function
immediately terminates and the control goes back to the caller.
Answer: True
3. True or False: A return statement must be the last statement in a function.
Answer: False
4. A(n) ____________________ is a function heading without the body of the function.
Answer: function prototype
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Class Discussion Topics
1. This chapter mentioned that function prototypes are useful for avoiding compilation
errors. Are there any other advantages of using function prototypes?
2. When designing the placement of a return statement(s) in a function, why is it a good
idea to return a value as soon as it is computed?
3. Briefly discuss how local declarations are stored in computer memory. Are there any
reasons to avoid using local declarations if it is possible to achieve the same result
without them? You may wish to use the functions on page 316 to facilitate the
discussion.
Additional Projects
1. Write a program in which you implement two math functions and call them from the
main function with a variety of test data. You may implement your own version of any
of the predefined functions in the C++ library (such as log), or another type of
arithmetic function, such as the factorial function. You may reuse functions if you have
already implemented them as part of a previous programming project.
2. Write a program that includes a function called displayTime() to output the current
time. You will call the predefined function ctime() in your function. Do some
research to determine how to use this function to retrieve the current time and display it
to the standard output device. Test your functions by writing the appropriate function
calls in the main function.
Additional Resources
1. C++ Notes: Functions:
www.fredosaurus.com/notes-cpp/90summaries/30funcsum.html
2. cmath Library:
www.cplusplus.com/ref/cmath/
3. ctime():
www.cprogramming.com/fod/ctime.html
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Key Terms
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Actual parameter: variable or expression listed in a call to a function
Body (of a function): code required to accomplish the task
Data type (of a function): return type of a value-returning function
Definition (of a function): includes the name of the function, a listing of the parameters
if any, the data type of each parameter, the data type of the value returned by the
function, and the code required to accomplish the task
Formal parameter: a variable declared in the function heading
Function header (heading): includes the name of the function, the number of
parameters if any, the data type of each parameter, and the data type of the value
returned by the function
Function prototype: function heading without the body of the function
Return type (of a function): type of the value that the function returns; also called the
data type of a function
Local declaration: declaration of a variable within a block of code for use only within
that block
Module: another name for a function
Parameter: may be formal or actual
Value-returning functions: functions that have a return type
Void functions: functions that do not have a data type