1. Chapter 10: Void Functions
Introduction to Programming with C++
Fourth Edition

2. Objectives Create and invoke a function that does not return a value
Pass information, by reference, to a function
Introduction to Programming with C++, Fourth Edition

3. More About Functions Programmers use functions for two reasons:
To avoid duplicating code in different parts of a program
To allow large and complex programs to be broken into small and manageable tasks
Introduction to Programming with C++, Fourth Edition

4. Creating Void Functions
Void function - a function that does not return a value after completing its assigned task
You might want to use a void function in a program simply to display information:
Example: title and column headings at the top of each page in a report
Introduction to Programming with C++, Fourth Edition

5. Creating Void Functions (continued)
Introduction to Programming with C++, Fourth Edition

6. Creating Void Functions (continued)
Differences between the syntax of a value-returning function and that of a void function:
The function header in a void function begins with the keyword void, rather than with a data type
The keyword void indicates that the function does not return a value
The function body in a void function does not contain a return expression; statement
Introduction to Programming with C++, Fourth Edition

7. Passing Variables
Most programming languages allow you to pass to the receiving function either:
The variable’s value (pass by value)
Its address (pass by reference)
Introduction to Programming with C++, Fourth Edition

8. Passing Variables by Value
Introduction to Programming with C++, Fourth Edition

9. Passing Variables by Reference
Passing a variable’s address (passing by reference) gives the receiving function access to the variable being passed
You pass a variable by reference when you want the receiving function to change the contents of the variable
Introduction to Programming with C++, Fourth Edition

10. Passing Variables by Reference (continued)
To pass a variable by reference to a C++ function:
Include an ampersand (&), called the address-of operator, before the name of the corresponding formal parameter in the function header
Introduction to Programming with C++, Fourth Edition

11. Passing Variables by Reference (continued)
Introduction to Programming with C++, Fourth Edition

12. Passing Variables by Value and by Reference
Introduction to Programming with C++, Fourth Edition

13. Passing Variables by Value and by Reference (continued)
Introduction to Programming with C++, Fourth Edition

14. Passing Variables by Value and by Reference (continued)
salary and raiseRate: passed by value because the receiving function needs to know the values stored in the variables, but does not need to change the values
raise and newSalary: passed by reference, because it is the receiving function’s responsibility to calculate the raise and new salary amounts and then store the results in these memory locations
Introduction to Programming with C++, Fourth Edition

15. Passing Variables by Value and by Reference (continued)
Introduction to Programming with C++, Fourth Edition

16. Passing Variables by Value and by Reference (continued)
Introduction to Programming with C++, Fourth Edition

17. Passing Variables by Value and by Reference (continued)
Introduction to Programming with C++, Fourth Edition

18. Summary
Void function - a function that does not return a value after completing its assigned task
Pass information by reference to a function
Function can change the variable that is passed in
Introduction to Programming with C++, Fourth Edition