1 C++ Functions

// The function computes and returns the gross pay // based on the pay rate and hours. Hours over // 40 will be paid 1.5 times the regular pay rate. float GrossPay(float payRate, float hours) { float total; if (hours > REG_HOURS) total = (hours - REG_HOURS)* OVER_TIME * payRate + REG_HOURS * payRate; else total = hours * payRate; return total; } // No input for payRate and hours // Parameters receive values on function call! 2

Passing Parameters const float REG_HOURS = 40.0; const float OVER_TIME = 1.5; int main() { float hours, rate, gross; cin >> rate >> hours; // rate: 12.5 // hours: 50 gross = GrossPay(rate, hours); // display result return 0; } int GrossPay(float payRate, float hours) { float total; if (hours > REG_HOURS) total = (hours - REG_HOURS) * OVER_TIME * payRate + REG_HOURS * payRate; else total = hours * payRate; return total; } main() GrossPay() Function call Passing parameters Returning to main() With return value 3

IN Parameter The value of the actual parameter is passed into the function and assigned to the formal parameters. float GrossPay(float payRate, float hours); int main() {... cin >> rate >> hours; // rate: 12.5 // hours: 45.5 gross = GrossPay(rate, hours);... } 4

IN Parameters int Largest(int num1, int num2, int num3); cin >> score1 >> score2 >> score3; max = Largest(score1, score2, score3); void DisplayResult(float avg, float max, float min); // Input scores and compute the highest, // lowest and average DisplayResult(avg, highest, lowest); // The function does output, but IN parameters! float sqrt(float x); 5

Function Parameters In The value of the actual parameter is passed into the function and assigned to the formal parameter. Out The value of formal parameter is passed out of the function and assigned to the actual parameter. InOut Both In and Out. 6

float GrossPay(float payRate, float hours); int main() { float hours, rate, gross; // Input values in main() cin >> rate >> hours; gross = GrossPay(rate, hours); // display result return 0; } // Q: Can we use a function to input rate and hours? 7

Write a function to input rate and hours Function Prototype Name: GetInput Type: void Cannot pass two values using the return statement Parameters: rate (payRate), hours (hoursWorked) type: float (Passing values back to calling function) (OUT parameters!) (&) void GetInput(float& payRate, float& hoursWorked); 8

float GrossPay(float payRate, float hours); void GetInput(float& payRate, float& hoursWorked); int main() { float hours, rate, gross; // Call function GetInput() to get two values GetInput(rate, hours); // Call function GrossPay to get one value gross = GrossPay(rate, hours); // display result return 0; } 9

Function Definition // // The function inputs payRate and hoursWorked and // pass both values back to the calling function. // Parameters: (out, out) // void GetInput(float& payRate, float& hoursWorked) { cout << "Enter pay rate: "; cin >> payRate; cout << "Enter hours: "; cin >> hoursWorked; return; } // The function does input with prompt, but OUT parameters! // How can it pass two values back? // Out Parameters: & // Statement return can pass only one value back! 10

// // The function computes and returns the gross pay // based on the pay rate and hours. Hours over // 40 will be paid 1.5 times the regular pay rate. // Parameters: (in, in) // float GrossPay(float payRate, float hours) { if (hours > REG_HOURS) payRate = (hours - REG_HOURS) * OVER_TIME * payRate + REG_HOURS * payRate; else payRate = hours * payRate; return payRate; } // No local variable // payRate is used to store the result 11

Reference and Value Parameters float GrossPay(float payRate, float hours); void GetInput(float& payRate, float& hoursWorked); Value parameter: No & The value of actual parameter is passed to the formal parameter Reference Parameter: & The address of actual parameter is passed to the formal parameter Does the actual parameter change its value when the corresponding formal parameter changes its value? Value parameter (no &): NO Reference parameter (&): YES 12

Value and Reference Parameters const float REG_HOURS = 40.0; const float OVER_TIME = 1.5; int main() { float hours, rate, gross; GetInput(rate, hours); gross = GrossPay(rate, hours); // display result return 0; } float GrossPay(float payRate, float hours) { if (hours > REG_HOURS) payRate = (hours - REG_HOURS) * OVER_TIME * payRate + REG_HOURS * payRate; else payRate = hours * payRate; return payRate; } main() GetInput() void GetInput(float& payRate, float& hoursWorked) { cout << "Enter pay rate: "; cin >> payRate; cout << "Enter hours: "; cin >> hoursWorked; return; } GrossPay() Passing parameters Passing parameters Addresses of rate and hours Return control With value Return control 13

Tracing Functions Input: HiC Notes\HiC\GrossPayInOutFuns.cpp 14

Tracing Functions Input: GetInput(rate, hours); // Reference parameters gross = GrossPay(rate, hours);// Value parameters main() GetInput() GrossPay() hours rate gross & payRate & hoursWorked hours payRate ? ? ? ? ? ? ? Addr of Addr of rate hours

Schedule Program 2 Grace Time: 9:30 PM, Today Style! Name conversion Quiz 4-2 Due 5 pm Monday Program 3 Two points Quiz Wednesday Two points progress Lab Thursday Discuss Friday 16

17 Prog2 Winner // The new route is the winner if (totalDistance < minTotalDistance && numDeiveries > maxDeiveries) // update winnerNum, // minTotalDistance and maxDeiveries // No winner for now else if (totalDistance =< minTotalDistance || numDeiveries >= maxDeiveries) // update winnerNum to -1 // minTotalDistance and maxDeiveries // The previous winner still winner else // do nothing

18 Prog2 Winner if (totalDistance < minTotalDistance && numDeiveries > maxDeiveries)... // No winner for now else if (totalDistance =< minTotalDistance || numDeiveries >= maxDeiveries) { winnerNum = -1; minTotalDistance = -1; maxDeiveries = -1; } Incorrect! Not Style!

19 Prog2 Winner // No winner for now else if (totalDistance =< minTotalDistance || numDeiveries >= maxDeiveries) { winnerNum = -1; if (totalDistance < minTotalDistance) minTotalDistance = totalDistance; if (numDeiveries > maxDeiveries) maxDeiveries = numDeiveries; } Correct! Update your Prog2 and submit again!

20 Prog2 Winner: Another Way if (totalDistance < minTotalDistance && numDeiveries > maxDeiveries)... else { if (totalDistance =< minTotalDistance) { winnerNum = -1; minTotalDistance = totalDistance; } // No else ! if (numDeiveries >= maxDeiveries) { winnerNum = -1; maxDeiveries = numDeiveries; } }

21 Prog2 Winner: Another Way if (routeNum == 1) { distWinnerNum = routeNum; delWinnerNum = routeNum; minTotalDistance = totalDistance; maxDeiveries = numDeiveries; } else { if (totalDistance < minTotalDistance) { distWinnerNum = routeNum; minTotalDistance = totalDistance; } else if (totalDistance == minTotalDistance) { distWinnerNum = routeNum; } // else prev distWinnerNum still winner // same if – else if for delWinnerNum }

Exercise Tracing Functions with In and Out Parameters GrossPayInOutParam.doc 22

Tracing Functions Input: GetInput(rate, hours); // Reference parameters gross = GrossPay(rate, hours);// Value parameters main() GetInput() GrossPay() hours rate gross & payRate & hoursWorked hours payRate ? ? ? ? ? ? ? Addr of Addr of rate hours