a function (procedure)

a function (procedure) ---- Func (arguments) --- Return value Return_type Func(parameters) code to perform a task (carry out an algorithm)

Parameters • Java parameters are either • primitive types - parameter is a copy of the argument (argument cannot be changed) • objects - parameter is an alias for the argument (argument can be changed) • C++ parameters are either • value parameters • reference parameters • constant reference parameters • array parameters

obj.myMethod (intArg, objArg); objArg number myObj 36 intArg activation record (memory space) created when myMethod is called 36 Java parameter passing public void myMethod (int number, SomeClass myObj) { --- --- }

C++ Parameters • C++ parameters are either • value - (type param_name) • parameter is a copy of the argument, thus argument cannot be modified • reference - (type & param_name) • parameter is an alias for the argument, thus argument is modified if parameter is modified • constant reference - (const type & param_name) • parameter is an alias for the argument, but compilerdisallows assignment to parameter

myFunction (v, r, cr); val 36 activation record (memory space) created when myFunction is called v r cr ref 36 25 6 constref C++ parameter passing void myFunction (int val, int & ref, const int & constref) { --- --- }

main Instruct GetEmployee Info GrossWages Compute NetPay Print EmpInfo Decomposition Example from Figure C.6 Using Functions on p.781

/* Program to compute wages for several employees. Written at ___________ by _________________- Input: Id-number, number of dependents, hours worked, and hourly rate for each of several employees Output: Id-number, hours worked, gross pay, taxes withheld and net pay ____________________________________________________*/ #include <iostream> #include <iomanip> using namespace std; void Instruct ( ); void GetEmployeeInfo (int & empNumber, int & dependents, double & hours, double & rate, bool & done); double GrossWages (int dependents, double hours, double rate); void ComputeNetPay (double grossPay, int dependents, double & tax, double & netPay); void PrintEmpInfo (int idNumber, double hours, double grossPay, double taxes, double netPay); int main ( ) { ----- }

int main ( ) { int idNumber, // employee's id-number numDependents; // number of dependents double hoursWorked, // hours worked this pay period hourlyRate, // dollars per hour grossPay, // pay before taxes taxWithheld, // amount of tax withheld netPay; // grossPay - tasWithheld bool endOfData; // signals end of data Instruct ( ); for ( ; ; ) { GetEmployeeInfo (idNumber, numDependents, hoursWorked, hourlyRate, endOfData); if (endOfData) break; // MUST BE CHANGED!! grossPay = GrossWages (numDependents, hoursWorked, hourlyRate); ComputeNetPay (grossPay, numDependents, taxWithheld, netPay); PrintEmpInfo (idNumber, hoursWorked, grossPay, taxWithheld, netPay); } return 0; }

int main ( ) { int idNumber, // employee's id-number numDependents; // number of dependents double hoursWorked, // hours worked this pay period hourlyRate, // dollars per hour grossPay, // pay before taxes taxWithheld, // amount of tax withheld netPay; // grossPay - tasWithheld // bool endOfData; // signals end of data Instruct ( ); while (GetEmployeeInfo (idNumber, numDependents, hoursWorked, hourlyRate)) { // if (endOfData) break; // TO BE CHANGED!! grossPay = GrossWages (numDependents, hoursWorked, hourlyRate); ComputeNetPay (grossPay, numDependents, taxWithheld, netPay); PrintEmpInfo (idNumber, hoursWorked, grossPay, taxWithheld, netPay) } return 0; }

bool GetEmployeeInfo (int & empNumber, int & dependents, double & hours, double & rate); Change Needed? void GetEmployeeInfo (int & empNumber, int & dependents, double & hours, double & rate, bool & done);

/* bool GetEmployeeInfo (int & empNumber, int & dependents, double & hours, double & rate) Purpose: read information for one employee Precondition(s): none Postcondition(s): The four parameters have been assigned values Returns: false if end of data reached; true otherwise --------------------------------------------------------------------------------------------*/ bool GetEmployeeInfo (int & empNumber, int & dependents, double & hours, double & rate) { cout << "\nEnter employee number (0 to stop): "; cin >> empNumber; if (empNumber == 0) return false; cout << "Enter # of dependents, hours worked, and hourly rate for " << empNumber << ": "; cin >> dependents >> hours >> rate; return true; }

/* double GrossWages (int dependents, double hours, double rate) Purpose: compute gross wages as determined by number of hours employee worked plus a dependency allowance for each dependent. Precondition(s): dependents, hours and rate >= 0 Postcondition(s): none Returns: Gross wages --------------------------------------------------------------------------------------------*/ double GrossWages (int dependents, double hours, double rate) { const double DEP_ALLOWANCE = 100; // bonus per dependent double wages; // wages earned if (hours <= 40) // no overtime wages = hours * rate; else // overtime wages = 40 * rate + 1.5 * rate * (hours - 40); return wages + DEP_ALLOWANCE * dependents; }

/* void Instruct ( ) Purpose: Display instructions to the user Precondition(s): none Postcondition(s): instructions have been displayed on the screen Returns: nothing **********************************************************************************/ /* void ComputeNetPay(double grossPay, int dependents, double & tax, double & netPay) Purpose: compute taxes withheld and net pay Precondition(s): grossPay and dependents are valid Postcondition(s): tax and netPay have been assigned computed values Returns: nothing ************************************************************************************/ /* void PrintEmpInfo( int idNumber, double hours, double grossPay double taxes, double netPay) Purpose: display payroll information regarding one employee Precondition(s): idNumber, hours, grossPay, taxes and netPay are valid Postcondition(s): payroll information has been displayed on the screen Returns: nothing *************************************************************************************/

Programming & Problem Solving Real world results Real world problem PROBLEM DOMAIN PROGRAM DOMAIN Representation of results Representation of real world problem Processing algorithms

10011100 Variables (data objects) • Components of a data object • name (programmer defined) • address (memory location) • type • value (determined by interpretation of the sequence of bits stored in memory) • type name [= value];

Types • predefined (built-in) vs programmer defined • simple (fundamental) vs structured • type of a data object determines • number of bytes used to store the value • interpretation of the bit pattern stored in those bytes • possible operations • data abstraction refers to the separation of the use of a data type from the implementation details

istream ostream iostream ifstream ofstream fstream string vector deque list stack queue map multimap set multiset bitset valarray C++ Types Fundamental Types Structured Types array Arithmetic void struct pointers union bool complex Integral Floating point (reals) float Characters Enumerations Integers double C++ Standard Library classes long double int char short int priority_queue unsigned char long int signed char unsigned unsigned short unsigned long

C++ arrays • groups data items of same type under one name • double Numbers[4]; • int List = {45, 63, 22}; • individual items accessed by indexing • Numbers[2] = 85.3; • first array element is at index position 0 • C++ arrays are not objects • no length data member • number of elements is determined either • at compile-time (both examples above) • at run-time (coming later)

List[0] List[1] List[2] b b+1 b+2 b+3 b+4 - - - - - - - - - - b+8 - - - - - - - - - - b+12 List 45 63 22 C++ array implementation • array name is a variable whose value is the base address of the array, i.e. a pointer variable • accessing an individual element involves calculating its address • base_address + index * element_size

Alternative Syntax • Given: int List = {45, 63, 22}; • first element can be accessed by • List[0]; • *List; // * is the dereferencing operator • second element can be accessed by • List[1]; • *(List + 1); • what is the value of List? • always use the indexing notation

const A N activation record (memory space) created when func is called 4 C++ array parameters void func (double A[ ], int N) { --- --- } arguments provided when func is called Numbers 3.2 2.1 5.9 7.0 N 4

C++ structs • struct - group of data items of different types • struct person { string Name; int Age;}; • person is a type grouping together 2 data members • person OneStudent; //represents 1 person • person Class[25]; //represents 25 persons • dot operator (.) used to access members • Class[i].Age • struct to struct assignments are legal • Class[i] = Class[i+1];

Creating New C++ Types • enumeration • allows defining your own set of values for a scalar type • typedef • allows for defining a synonym or alias for an existing type • struct • allows a variable to have multiple values of different types • class • allows encapsulating data members and operations

Enumeration • used to make a program more readable • associates a set of programmer defined values with the integer values 0, 1, 2, - - • Example • enum Suit {CLUBS, SPADES, HEARTS, DIAMONDS}; • Suit mySuit = HEARTS; • if (mySuit == SPADES) --- • switch (mySuit) { case CLUBS: ---- case SPADES: ---

typedef statement • used to declare a new name (synonym) for an already existing type • const int SIZE = 100; • typedef int intArrayType[SIZE]; • intArrayType numberList; • usually given global (file) scope • used to make a program easier to modify

C++ strings • early versions of C++ used “C-style strings” • array of char with a special character (null character) marking the end • <string.h> or <cstring> have functions to manipulate C-style strings • C++ standard library provides the class string • #include <string> • use C++ string class, not C-style strings • see Ch.3 sec.4 for information and examples; also TableD.4

a function (procedure)