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Electrical and Computer Engineering
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Value-Returning Functions
- A call to a value-returning function is part of an
expression.
- A value-returning function is used when there is
only one result returned by a function and that
result is to be used directly in an expression.
- A value-returning function returns one value, not
through a parameter but by means of a return
statement.
Electrical and Computer Engineering
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Value-Returning Function Example
int Power (/* in / int x, // Base number / in */ int n) // Power to raise base to { int result; // Holds intermediate powers of x result = 1; while (n > 0) { result = result * x; n--; } return result; } Usage y = Power(5, 3)
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UAH CPE 112
Another Value-Returning
Function Example
#include using namespace std;
int Min (int val1, int val2, int val3);
int main() { int num1; int num2; int num3; int min_num;
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UAH CPE 112
Another Value-Returning
Function Example
cout << "Please enter an integer value for num1: " << endl; cin >> num1; cout << "Please enter an integer value for num2: ” << endl; cin >> num2; cout << "Please enter an integer value for num3: " << endl; cin >> num3;
min_num = Min(num1, num2, num3);
cout << "The minimum number of the three entered is ” << min_num << endl; }
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Another Value-Returning
Function Example
int Min (int val1, int val2, int val3) { int result;
result = val1;
if (val2 < result) result = val2; if (val3 < result) result = val3;
return result; } Electrical and Computer Engineering 6 of 24
UAH CPE 112
Revisiting the Power Function
#include #include using namespace std;
float power (int base, int exponent);
int main() { float result; int base; int exponent;
cout << "Please enter integer base value " << endl; cin >> base;
Electrical and Computer Engineering
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Revisiting the Power Function
cout << "Please enter integer exponent value " << endl; cin >> exponent;
result = power(base, exponent); cout << base << " raised to the " << exponent << " power is " << result << endl; }
Electrical and Computer Engineering
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Revisiting the Power Function
float power (int base, int exponent) { int i =1; float result = 1.0;
while (i <= abs(exponent)) { result = result * base; i++; } if (exponent < 0) result = 1.0/result; return result; }
Electrical and Computer Engineering
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UAH CPE 112
Problem-Solving Case Study
(Starship Weight and Balance)
- Problem: Write a program that determines the
weight and center of gravity of a new plane, based
on the number of crew members and passengers as
well as the weight of the baggage, closet contents,
and fuel.
- Input: Number of crew members, number of
passengers, weight of closet contents, baggage
weight, fuel in gallons.
- Output: Total weight, center of gravity.
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Starship Weight and Balance (continued)
- Discussion: Sum all of the weights, using the
standard average weight of a person of 170
pounds, and the fact that a gallon of fuel weighs
6.7 pounds.
- totalWeight = emptyWeight + (crew + passengers) *
170 + baggage + closet + fuel * 6.
- centerofGravity = (emptyMoment + crewMoment +
passengerMoment + cargoMoment +
fuelMoment)/totalWeight
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Main (Level 0)
Get data
Set totalWt = EMPTY_WEIGHT + (passengers +
crew) * 170 + baggage + closet + fuel * 6.
Set centerof Gravity = (CrewMoment(crew) +
PassengerMoment(passengers) + CargoMoment(closet,
baggage) + FuelMoment(fuel) + EMPTY
_MOMENT)/totalWt
Print totalWt, centerof Gravity
Print warning
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Level 1 Functional Decomposition
Get Data (Out: crew, passengers, closet, baggage, fuel)
Prompt for numer of crew, number of passengers, weight in closet
and baggage compartments, and gallons of fuel
Read crew, passengers, closet, baggage, fuel
Echo print the input
CrewMoment (In: crew) Out Function Value
Return crew * 170 * 143
Cargo Moment (In: closet, baggage) Out: Function value
Return closet * 182 + baggage * 386
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Case Study Implementation
float CrewMoment( /in/ int crew ) // Number of crew members
// Computes the crew moment arm in inch-pounds from the number of // crew members. Global constant PERSON_WT is used as the weight // of each crew member // Precondition: // crew == 1 OR crew == 2 // Postcondition: // Function value == Crew moment arm, based on the crew // parameter
{ const float CREW_DISTANCE = 143.0; // Distance to crew seats // from front
return float(crew) * PERSON_WT * CREW_DISTANCE; } Electrical and Computer Engineering
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Case Study Implementation
float PassengerMoment( /in/ int passengers ) { const float ROW1_DIST = 219.0; // Distance to row 1 seats const float ROW2_DIST = 265.0; // Distance to row 2 seats const float ROW3_DIST = 295.0; // Distance to row 3 seats const float ROW4_DIST = 341.0; // Distance to row 4 seats float moment = 0.0; // Running total of moment if (passengers > 6) // For passengers 7 and 8 { moment = moment + float (passengers - 6) * PERSON_WT * ROW4_DIST; passengers = 6; // 6 remain } if (passengers > 4).. // For passengers 5 and 6 . return moment; }
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Case Study Implementation
float CargoMoment( /in/ int closet, // Weight in closet /in/ int baggage ) // Weight of baggage
// Computes the total moment arm for cargo loaded into the // front closet and aft baggage compartment // Precondition: // 0 <= closet <= 160 && 0 <= baggage <= 525 // Postcondition: // Function value == Cargo moment arm, based on the closet // and baggage parameters
{ const float CLOSET_DIST = 182.0; // Distance to closet const float BAGGAGE_DIST = 386.0; // Distance to baggage return float(closet) * CLOSET_DIST + float(baggage) * BAGGAGE_DIST; } Electrical and Computer Engineering
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Case Study Implementation
float FuelMoment( /* in */ int fuel ) // Fuel in gallons { float fuelWt; // Weight of fuel in pounds float fuelDistance; // Distance from front of plane
fuelWt = float(fuel) * LBS_PER_GAL; if (fuel < 60) fuelDistance = float(fuel) * 314.6; else if (fuel < 361) fuelDistance = 305.8 + (-0.01233 * float(fuel - 60)); else if (fuel < 521) fuelDistance = 303.0 + ( 0.12500 * float(fuel - 361)); else fuelDistance = 323.0 + (-0.04444 * float(fuel - 521)); return fuelDistance * fuelWt; }
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Testing & Debugging – Stubs
- A stub is has the same name and interface as a function
that actually would be called by the part of the program
being tested, but it is usually much simpler
- Example void GetYear (/inout/ ifstream& dataIn, // Input file /out/ string& year) //Four digits of year
// Stub for GetYear function in the ConvertDates program
{ cout << “Get Year was called here. Returning \”1949\”.” << endl; year = “1948”; }
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Testing & Debugging - Drivers
- A driver is a simple main function which cals a function
being tested and permits direct control of testing.
float FuelMoment (int); int main() { int testVal; cout << “Fuel moment for gallons from 10 – 565 in steps” << “of 15:” << endl; testVal = 10; while (testVal <= 565) { cout << FuelMoment(testVal) << endl; testVal = testVal + 15; } }
