1. An Introduction to Programming with C++ Fifth Edition
Chapter 9
Value-Returning Functions

2. Objectives Raise a number to a power Generate random numbers
Create and invoke a function that returns a value
Pass information, by value, to a function
An Introduction to Programming with C++, Fifth Edition

3. Objectives (continued)
Write a function prototype
Understand a variable’s scope and lifetime
Use the .NET C++ Math::Pow() method
Generate random integers in .NET C++
An Introduction to Programming with C++, Fifth Edition

4. Concept Lesson Functions Value-Returning Functions
Raising a Number to a Power
Generating Random Numbers
Creating Program-Defined Value-Returning Functions
Processing a Function
An Introduction to Programming with C++, Fifth Edition

5. Functions A function is a block of code that performs a task
A C++ program contains at least one function: main()
Most contain many more
Programmers use functions because they:
Allow programmer to avoid duplicating code
Allow programs to be broken into manageable tasks
Functions can be categorized into:
Value-returning functions
Void functions
An Introduction to Programming with C++, Fifth Edition

6. Value-Returning Functions
A value-returning function returns precisely one value after completing its assigned task
Usually returned to the statement that called function
Typically, statement displays return value, uses it in a calculation, or assigns it to a variable
Some value-returning functions are built into C++
E.g., getline() and toupper()
An Introduction to Programming with C++, Fifth Edition

7. Raising a Number to a Power
You use pow( )to raise a number to a power and return result as a double number
An Introduction to Programming with C++, Fifth Edition

8. Generating Random Numbers
A pseudo-random number generator produces a sequence of numbers that meet certain statistical requirements for randomness
Numbers are chosen with equal probability from a finite set of numbers
Chosen numbers are sufficiently random for practical purposes
rand() returns an integer greater than or equal to zero and less than or equal to RAND_MAX
RAND_MAX is always at least 32,767
An Introduction to Programming with C++, Fifth Edition

9. Generating Random Numbers (continued)
An Introduction to Programming with C++, Fifth Edition

10. Generating Random Numbers (continued)
An Introduction to Programming with C++, Fifth Edition 10

11. Generating Random Numbers (continued)
An Introduction to Programming with C++, Fifth Edition

12. Generating Random Numbers (continued)
An Introduction to Programming with C++, Fifth Edition

13. Generating Random Numbers (continued)
You should initialize the random number generator in each program in which it is used
Otherwise, it will generate the same series of numbers each time
Use the srand() function
You must provide a seed
Integer that represents the starting point for the random number generator
Usually use time(): returns current time as seconds elapsed since midnight January 1, 1970
An Introduction to Programming with C++, Fifth Edition

14. Generating Random Numbers (continued)
An Introduction to Programming with C++, Fifth Edition

15. Random Numbers Program: Displaying Random Addition Problems
Program displays five random addition problems on the screen
After displaying an addition problem, it allows user to enter the answer to the problem
It checks whether the user’s answer is correct
“Correct!”
“Sorry, the sum is X”
An Introduction to Programming with C++, Fifth Edition

16. Random Numbers Program: Displaying Random Addition Problems (continued)
An Introduction to Programming with C++, Fifth Edition

17. Random Numbers Program: Displaying Random Addition Problems (continued)
An Introduction to Programming with C++, Fifth Edition

18. Random Numbers Program: Displaying Random Addition Problems (continued)
An Introduction to Programming with C++, Fifth Edition

19. Creating Program-Defined Value-Returning Functions
You can create your own value-returning functions
Program-defined functions
A function definition is composed of:
Function header
Function body
An Introduction to Programming with C++, Fifth Edition

20. Creating Program-Defined Value-Returning Functions (continued)
An Introduction to Programming with C++, Fifth Edition

21. Function Header Function header: first line in a function definition
Does not end with a semicolon
Not considered a C++ statement
Begins with returnDataType
Next comes the name of the function
Naming rules are the same as for naming variables
Name usually begins with a verb
Also has an optional parameterList enclosed in ()
Lists data type and name of formal parameters
Formal parameters store the information passed to the function when it is invoked
An Introduction to Programming with C++, Fifth Edition

22. Passing Information to a Function
Items passed to a function are actual arguments
Can be a variable, named constant, literal constant, or keyword
You can pass a variable:
by value (a copy of the value is passed), or
by reference (the variable address is passed)
Examples
calcRectangleArea(2, 3)
calcRectangleArea(length, width)
default
pass by value
An Introduction to Programming with C++, Fifth Edition

23. Function Body
Function body contains instructions the function follows to perform its assigned task
Begins with { and ends with }
The last statement is usually return expression;
expression represents the value the function returns to the statement that called it
return statement alerts computer that the function has completed its task
Data type of expression must agree with the returnDataType specified in function header
An Introduction to Programming with C++, Fifth Edition

24. Using a Function Prototype
If a function definition appears below main(), you must enter a function prototype above main()
Prototype specifies function’s name, data type of return value and of each formal parameter
Usually after #includes and usings
An Introduction to Programming with C++, Fifth Edition

25. Processing a Function
When the computer processes a statement containing a program-defined function:
It locates the function’s code
Passes values of actual arguments to function
Function receives values and stores them in the memory locations listed in its parameterList
Function code is processed
Return value is returned to calling function
An Introduction to Programming with C++, Fifth Edition

26. Processing a Function (continued)
An Introduction to Programming with C++, Fifth Edition

27. Processing a Function (continued)
An Introduction to Programming with C++, Fifth Edition

28. Processing a Function (continued)
An Introduction to Programming with C++, Fifth Edition

29. Processing a Function (continued)
An Introduction to Programming with C++, Fifth Edition 29

30. The Scope and Lifetime of a Variable
A variable’s scope indicates where in the program it can be used
Local or global
Local variables are declared within a function or appear in a function’s parameterList
Global variables are declared outside of any function and remain in memory until program ends
Avoid using global variables in your programs
A variable’s lifetime indicates how long it remains in memory
An Introduction to Programming with C++, Fifth Edition

31. The Bonus Calculation Program
Program calculates and displays a 5% bonus amount
Based on the amount of sales entered by the user
Program uses two value-returning functions:
getSales()
calcBonus()
An Introduction to Programming with C++, Fifth Edition

32. The Bonus Calculation Program (continued)
An Introduction to Programming with C++, Fifth Edition

33. The Bonus Calculation Program (continued)
An Introduction to Programming with C++, Fifth Edition

34. The Bonus Calculation Program (continued)
An Introduction to Programming with C++, Fifth Edition

35. The Bonus Calculation Program (continued)
An Introduction to Programming with C++, Fifth Edition

36. The Bonus Calculation Program (continued)
An Introduction to Programming with C++, Fifth Edition 36

37. The Bonus Calculation Program (continued)
An Introduction to Programming with C++, Fifth Edition

38. Summary Programmers use functions because they:
Allow programmer to avoid duplicating code
Allow programs to be broken into manageable tasks
Functions can be value-returning or void
E.g., pow() and rand() are value-returning functions
A function definition has a function header and a body
Header specifies return data type, function name, and (optional) parameterList enclosed in parentheses
By default, variables are passed to a function by value
An Introduction to Programming with C++, Fifth Edition

39. Summary (continued) The function body contains instructions for a task
Enclosed in braces
You must include a function prototype for each function defined below main()
A variable’s scope can be either local or global
Indicates where in a program a variable can be used
If multiple memory locations have same name, and it appears in a statement, the computer uses the position of the statement within the program to determine which memory location to use
An Introduction to Programming with C++, Fifth Edition

40. Application Lesson: Using Value-Returning Functions in a C++ Program
Lab 9.1: Stop and Analyze
Lab 9.2:
Create a program to calculate and display the monthly payments of a loan
Lab 9.3:
Modified program should allow user to enter interest rates either as a whole or as a decimal number
Lab 9.4: Desk-Check Lab
Lab 9.5: Debugging Lab
An Introduction to Programming with C++, Fifth Edition