An Introduction to Programming with C++ Fifth Edition

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-DefinedValue-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-DefinedValue-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. default 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) 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 returnexpression; • 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() • Prototypespecifies 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