1. Chapter 9: Value-Returning Functions
Introduction to Programming with C++
Fourth Edition

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
Write a function prototype
Understand a variable’s scope and lifetime
Introduction to Programming with C++, Fourth Edition

3. Functions Functions: Value returning functions return a value
Allow programmers to avoid duplicating code in different parts of a program
Allow large and complex programs to be broken into small and manageable tasks
Value returning functions return a value
Void functions do not return a value
Introduction to Programming with C++, Fourth Edition

4. Raising a Number to a Power
pow() function:
Raises a number to a power
Returns the result as a double number
Is used to perform exponentiation
Program must contain the #include <cmath> directive and the using std::pow; statement
Introduction to Programming with C++, Fourth Edition

5. Syntax and Examples of the pow() Function
Introduction to Programming with C++, Fourth Edition

6. Generating Random Numbers
Most programming languages have a built-in function for generating random numbers
In C++, the random number generator is the rand() function
It returns an integer that is greater than or equal to 0, but less than or equal to RAND_MAX
You must initialize the random number generator in each program in which it is used
You initialize the random number generator using the srand() function
Introduction to Programming with C++, Fourth Edition

7. Generating Random Numbers (continued)
Introduction to Programming with C++, Fourth Edition

8. Generating Random Numbers (continued)
Introduction to Programming with C++, Fourth Edition

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

10. Creating Program-Defined Value-Returning Functions
Introduction to Programming with C++, Fourth Edition

11. Function Header
The function header is the first line in a function definition
It specifies:
The type of data the function returns (if any)
The function’s name
An optional parameterList
Introduction to Programming with C++, Fourth Edition

12. Function Header (continued)
Items of information you send (pass) to a function are called actual arguments
When a variable is passed by value, only the value stored in the variable is passed
When a variable is passed by reference, the address of the variable in memory is passed
Variables in C++ are automatically passed by value
Introduction to Programming with C++, Fourth Edition

13. Function Header (continued)
Each memory location listed in the parameterList is referred to as a formal parameter
The number of formal parameters included in the parameterList should agree with the number of actual arguments passed to the function
The data type and position of each formal parameter in the parameterList must agree with the data type and position of its corresponding actual argument in the argumentList
Introduction to Programming with C++, Fourth Edition

14. Function Body The function body:
Contains the instructions the function must follow to perform its assigned task
Begins with the opening brace ({) and ends with the closing brace (})
Last statement of a value-returning function is:
return expression;
return statement alerts the computer that the function has completed its task, and it ends the function
Introduction to Programming with C++, Fourth Edition

15. Using a Function Prototype
Function prototype - a statement that specifies the function’s name, the data type of its return value (if any), and the data type of each of its formal parameters
Programs have one function prototype for each function defined below the main() function
Function prototypes are normally placed at the beginning of the program, after the #using and using directives
Introduction to Programming with C++, Fourth Edition

16. Processing a Function
Call a program-defined function the same way as you call a built-in function, by including its name and actual arguments (if any) in a statement
If a function call has an argumentList, the values of the actual arguments are passed (assuming passed by value) to the called function
Function receives these values and stores them in the memory locations listed in parameterList
Introduction to Programming with C++, Fourth Edition

17. Processing a Function (continued)
Introduction to Programming with C++, Fourth Edition

18. The Scope and Lifetime of a Variable
Variable’s scope - indicates which portions of a program can use the variable (can be either local or global)
Variable’s lifetime - indicates how long the variable remains in the computer’s memory
Local variables - variables declared in a function, and those that appear in a function’s parameterList
Introduction to Programming with C++, Fourth Edition

19. The Scope and Lifetime of a Variable (continued)
Global variables:
Are declared outside of any function
Remain in memory until the program ends
Can be used by any statement in the program
Global variables allow unintentional errors to occur when a function that should not have access to the variable inadvertently changes it
Avoid using global variables in your programs
Introduction to Programming with C++, Fourth Edition

20. Summary Functions allow: Math functions include:
Large and complex programs to be broken into small and manageable tasks
Code to be reused
Math functions include:
Raising a number to a power
The random number generator
Introduction to Programming with C++, Fourth Edition

21. Summary (continued) Value returning functions return a value
Void functions do not return a value
Pass information by value to a function
Variables can be either local or global in scope
Introduction to Programming with C++, Fourth Edition