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Value Returning Functions

// Function prototype int Largest(int num1, int num2, int num3);

Function Name Type Parameters Type of parameters Formal parameters

// More examplesfloat sqrt(float x);char myFunction(float param1, int param2, char param3);

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Function Calls

// Function prototypeint Largest(int num1, int num2, int num3);

// Function callsmax = Largest(score1, score2, score3);// Must follow the prototype!// actual parameters are different from formal parameters

max = Largest(int score1, int score2, int score3);// Do not include type for actual parameters!

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Function Calls

// Function prototype

float GrossPay(float payRate, float hours)

cin >> hours >> rate;

// Function callsgross = GrossPay(rate, hours);

gross = GrossPay(hours, rate);// No Error// But incorrect result

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Function Calls

// Function prototypefloat sqrt(float x);

// Function callscout << “Square Root: ” << sqrt(delta);

sqrt(delta);// Error: Must use the return value

result = sgrt(delta);// Good!

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Function Calls// Function prototypechar myFunction(float param1, int param2, char param3);

char charVal;

charVal = myFunction(50.57, 48, ‘M’);// Valid Invalid

charVal = myFunction(50.57, 48);// Valid Invalid

charVal = myFunction(49, 50.57, ‘M’);// Valid Invalid

charVal = myFunction(50.57, 48, “M”);// Valid Invalid

myFunction(50.57, 48, ‘M’);// Valid Invalid

cout << myFunction(50.57, 48, ‘M’);// Valid Invalid

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VOID Functions

Write a C++ function to display max, min and average.

Function name DisplayResult

Function type void (does not return any value)

Function parameters How many? max, min, avg Type of each parameters int, int, float float, float, float

void DisplayResult(float avg, float max, float min);

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VOID Functionsvoid DisplayResult(float avg, float max, float min);

int main() { float score, avg, highest, lowest; int numScores, loopCount = 0;

// input scores

// Compute avg, highest and lowest

// output results DisplayResult(avg, highest, lowest);

return 0; }

// Decompose a program into smaller functions// Programming Rule: each function can have at most 30 lines!

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VOID Functionsvoid DisplayResult(float avg, float max, float min);

// Programming Rules: Each function must have a description! // ------------------------------------------------------------// The function displays avg, max and min in required format. // ------------------------------------------------------------void DisplayResult(float avg, float max, float min) { cout << fixed << showpoint << setprecision(2);

cout << endl << endl << "The average score: " << setw(8) << avg << “.\n” << "The highest score: " << setw(8) << max << “.\n” << "The lowest score : " << setw(8) << min;

// return control, no value return; }

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Functions without Parameters void UserInstruction();

int main() { float score, avg, highest, lowest; int numScores, loopCount = 0;

UserInstruction();

// input

// process

DisplayResult(avg, highest, lowest);

return 0; }

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// Programming Rules: Each function must have a description!

// -----------------------------------------------------// The function displays user instructions. // -----------------------------------------------------void UserInstruction() { cout << endl << endl << "The program process all scores of one section " << endl << "of a class. The first input is the number of " << endl << "scores. All scores must be in the range of " << endl << "0.0 and 60.0, inclusive." << endl << endl;

return; }

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Examplevoid DisplayMenu();

int main(){ … DisplayMenu(); …}

void DisplayMenu(){ cout << “\nM or m to convert Meters to Inches” << …

return;}

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Scope of Variables

The region of code where it is legal to reference (use) an identifier.

• Local Scope

• Global Scope

• Class Scope

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Code BlockBetween a pair of matching braces The body of a function

int main(){ int alpha = 10;

// A block for if statement if (alpha > 3) { int n; cin >> n; alpha += 3; } return 0;}

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Local Scope

The scope of an identifier declared inside a block extends from the point of declaration to the end of that block.

int main()

{

int alpha = 10;

// A code block

if (alpha > 3)

{

int num;

cin >> num;

alpha += num;

}

cout << “num = ” << num;

// Run time error!

return 0;

}

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Global Scope

The scope of an identifier declared outside all functions (and classes) extends from the point of declaration to the end of the entire source file.

Programming Rules:

No global variables!

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Class Scope

Later this semester!

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Scope of Function Parameters

• Formal parameters

Local scope

Same as local variable

Cannot reference it outside the function

Receive values on function call

• Actual parameters (no global variables)

Local scope

Cannot reference it inside the called function

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Examplefloat DoIt(int num, char op);

int main(){ int base; float result; char choice;

cout << “Enter a number: ”; cin >> base; cout << “C for Cube and S for Square Root: ”; cin >> choice;

while (choice != ‘C’ && choice != ‘S’) { cout << “C for Cube and S for Square Root: ”; cin >> choice; }

result = DoIt(base, choice);

cout << “The result: ” << result;

return 0;}

// ----------------------------// Precondition: op is ‘C’ or ‘S’// Postcondition: the cube of// num is computed when op is// ‘C’, and square root of num// is computed when op is ‘S’.// ------------------------------float DoIt(int num, char op){ if (op == ‘C’) result = pow(num, 3); else result = sqrt(num); return result;}

// What is wrong?// Result not declared in the // function!

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Precondition and Postconditionint DoIt(int num, char op);

int main(){ int base; float result; char choice;

cout << “Enter a number: ”; cin >> base; cout << “C for Cube and S for Square: ”; cin >> choice;

while (choice != ‘C’ && choice != ‘S’) { cout << “C for Cube and S for Square: ”; cin >> choice; }

result = DoIt(base, choice);

cout << “The result: ” << result;

return 0;}

// ------------------------------// Precondition: op is ‘C’ or ‘S’// Postcondition: the cube of// num is computed when op is// ‘C’, and square root of num// is computed when op is ‘S’.// ------------------------------int DoIt(int num, char op){ float result; if (op == ‘C’) result = pow(num, 3); else result = sqrt(num); return result;}

// The two variables // result have the same // name, but different!

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Parameter Names

• Meaningful names

• Formal and actual parameters can have the same name

• They are different variables in different scopes

• Normally they have different names

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Lifetime of a Variable

• Lifetime

The period of time during program execution when an identifier has memory allocated to it.

• Automatic variables

A variable for which memory is allocated and deallocated when control enters and exits the block it is declared.

• Static variables

A variable for which memory remains allocated throughout the execution of the entire program.

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Program 2

• Due 9:30 PM Today• Grace date Friday

Send email to me• Style

• Lab 4: Thursday

Exercise: Tracing Function Call

Exercise\GrossPayFunction.doc

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Tracing on GrossPay

Input values: 10 45

main() GrossPay() hours rate gross payRate hours pay

? ? ? ? ? ?

45 10

10 45

475

475