Functions g g Data Flow g Scope local global part II g Global Resolution Operator part II

Data Flow Data flow is the direction of the information flow between the function and its caller. Adding data flow documentation to the function interface is helpful. The flow could be into a function, out of a function or both.

Parameter and Data Flow /* in */ 4 pass data into a function/* in */ /* out */ 4 pass data out of a function/* out */ /* inout */ 4 pass data into and out of a function/* inout */

Examples void myFunction( /* in */ double nana, /* in */ int count) void yourFunction( /* out */ int& num1, /* out */ int& num2) void ourFunction( /* in */ int alpha, /* inout */ int& beta) Parameter and Data Flow

, To be certain a function does what you want it to do, write value of variables as you enter and exit a function., Put the output statement into a function and call it whenever you need it. void ShowIt(void) { cout<< var1<< ‘\t’ <<var2<< ‘\t’ <<var3<< ‘\n’; } *

Parameter and Data Flow Flow In int media( /* in */ int cow) { cout << “Ten * cow = “ << cow*10; return (2*cow +5); } int media( /* in */ int cow) { cow = 2 * cow; return (2*cow +5); } & out & *

Parameter and Data Flow Flow Out void media( /* out */ float& delta, /* out */ float& epsilon ) { delta = 1.0; epsilon = ; } epsilon = epsilon ; * inout inout epsilon = epsilon ; epsilon = epsilon ;

Parameter and Data Flow Flow In and Out void update( /* inout */ int& javel, /* inout */ int & grenelle ) { javel = 3 * javel; grenelle++; }

Data Flow - Example #include void getTemp(double&); void activity(double); void convertCtoF(double&); void main(void) { double temperature; getTemp(temperature); activity(temperature); }

Data Flow - Example void getTemp(/* */ double& temp){ cout<<"Enter the temperature in degrees C: "; cin>> temp; cout<<"The current temperature is " <<temp<<" degrees celsius."<<endl; convertCtoF(temp);} void convertCtoF( /* */ double& temp){ temp=(1.8)*temp +32; cout<<"This equals "<<temp <<" degrees Fahrenheit."<<endl;} out inout *

Data Flow - Example void activity(/* */ double temp){ cout<<"The recommended activity is "; if(temp>85) cout<<"swimming."<<endl; else if(temp>70) cout<<"tennis."<<endl; else if(temp>35) cout<<"golf."<<endl; else if(temp>10) cout<<"skiing."<<endl; else cout<<"dancing."<<endl;} in *

Data Flow data flowparameter-passing for a parametermechanism incomingpass-by-value outgoingpass-by-reference incoming/outgoingpass-by-reference

I/O Example void main(void) { 1 int red, blue; 2 void Mix( int&, int ); // prototype 3 int Blend( int, int ); // prototype 4 red = 5; 5 blue = Blend(3, red + 1); 6 Mix(red, blue); 7 cout << red << ' ' << blue << '\n'; 8 Mix(red, blue + red); 9 cout << red << ' ' << blue << '\n'; 10 Mix(red, Blend(blue, red)); 11 cout << red << ' ' << blue << '\n'; }

I/O Example M void Mix( int& green, int yellow) { M1 int purple; M2 cout << “enter Mix “ << green << ‘ ‘ << yellow << ‘\n’; M3 purple = green + yellow; M4 yellow = purple + yellow; M5 green = purple; M6 cout << “leav Mix “ << green << ‘ ‘ << yellow << ‘\n’; }

I/O Example B int Blend( int red, int green ) { B1 int yellow; B2 cout << “enter Blend “ << red <<‘ ‘ << green << ‘\n’; B3 yellow = red + green; B4 cout << “leave Blend “ << red <<‘ ‘ << green << ‘\n’; B5 return (yellow + 1); }

void Mix( /* ______ */ int& green, /* ______ */ int yellow ) int Blend( /* ______ */ int red, /* ______ */ int green ) I/O Example inout in * *

B B1 - B5 6 M M1 - M6 I/O Example * * 7 8 M M1 - M M B B1 - B5 M1 - M6 11 The lines are executed in this order.

I/O Example MixmemoryMain greenred blue yellowpurple

Mix Blend Main enter Blend 3 6 leave Blend 3 6 enter Mix 5 10 leave Mix enter Mix leave Mix enter Blend leave Blend enter Mix leave Mix *

Scope A function is like a black box: You know what goes in and what comes out, but you do not know what happens inside the box.

Scope The section of the program where the variable is valid (known or visible). local = available to only one function global = available several functions

Scope block Local: The scope of an identifier declared inside a block extends from the point of declaration to the end of that block. Global: The scope of an identifier declared outside all functions and classes extends from the point of declaration to the end of the source file. *

Local Variables / declared within a function definition / private to a function definition / variables in different functions are totally independent / different functions can have variables with the same names; however, each variable will have its own memory address * *

int x = 3; int x = 3;// global because before main void main(void) {// no variables local to main( ) void myfunction( );// prototype cout <<"x = "<<x<<" before the function call.\n"; myfunction( ); cout <<"x = "<<x<<" after the function call.\n"; } void myfunction( ) { int r;// local to myfunction( ) r = ++x; cout <<"r = "<<r<<" within the function.\n"; }

Scope OUTPUT x = 3 before the function call. r = 4 within the function. x = 4 after the function call.

Example Example - ReadValues void main(void) { int a, b, c; float avg; void ReadValues( int&, int&, int& ); void Adjust( int&, int&, int& ); float Average( int, int, int ); void WriteResults( int, int, int, int, float ); ReadValues(a, b, c); Adjust(a, b, c); avg = Average(a, b, c); WriteResults(a, b, c, a + b + c, avg); }

Example Example - ReadValues 1.main declares and calls ReadValues 2.ReadValues declares and calls ReadOne [3x] 3.main declares and calls Adjust 4.main declares and calls Average 5.main declares and calls WriteResults * *

Example Example - ReadValues void ReadValues( /* */ int& x, /* */ int& y, /* */ int& z ) { void ReadOne( char, int& ); ReadOne('1', x ); ReadOne('2', y ); ReadOne('3', z ); return; } * out

Example Example - ReadOne void ReadOne( /* */ char number, /* */ int& item ) { cout << "Enter value " << number << ": "; cin >> item; return; } * in out

Example Example - Adjust void Adjust( /* */ int& i, /* */ int& j, /* */ int& k ) { int smallest; smallest = i; if (j < smallest) i = i - smallest; smallest = j; j = j - smallest; if (k < smallest) k = k - smallest; smallest = k; return; } * inout

Example Example - Average float Average( /* */ int item1, /* */ int item2, /* */ int item3 ) { int total; total = item1 + item2 + item3; return float(total) / 3; } * in

Example Example - WriteResults void WriteResults( /* */ int item1, /* */ int item2, /* */ int item3, /* */ int total, /* */ float average ) { cout << "Adjusted values: " << item1 << ", " << item2 << ", " << item3 << '\n' << "Sum: " << total << " Average: " << average << '\n'; return; } * in

ReadValuesAdjustAverageWriteResults ReadOne Main Enter value 1: 23 Enter value 2: 56 Enter value 3: 78 Adjusted values: 0, 33, 55 Sum: 88 Average:

global void swap(int, int);// a global function void main(void) {int x = 5, y = 10; 1. cout <<“Main-before swap, x: “<<x<<" y: "<<y<< '\n'; swap(x, y); 2. cout <<"Main-after swap, x: "<<x<<" y: "<<y<<'\n'; } void swap(int x, int y) {int temp; 3. cout <<"Swap-before swap, x: "<<x<<" y: "<<y<<'\n'; temp = x;x = y;y = temp; 4. cout <<"Swap-after swap, x: "<<x<<" y: "<<y<<'\n'; }

Scope OUTPUT 1. Main-before swap:x: 5y: Swap-before swap:x: 5 y: Swap-after swap:x: 10 y: 5 2. Main-after swap:x: 5 y: 10

void Block1(int, char &); void Block2( ); int a1;// global char a2; // global int main() {... } Scope within a Block slide 1 of 2

void Block1(int a1, char &b2) // prevents access { // to global a1 int c1;// local to Block1 int d1; // local to Block1 }} slide 2 of 2 slide 2 of 2 *... void Block2() { int a1;// prevents access to global a1 int b1;// local to Block2 while (…) // Block3 { // Block3 int c1;// local to Block3 int b2;// prevents non-local access } }// to b2 in Block1...

Scope within a block - Ex. 1 predict the output void scope2(void);// function prototype void main(void) int v=100; {int v=100; cout <<"v BEFORE function = "<<v<<'\n'; scope2(); cout <<"v AFTER function = "<<v<<'\n'; } slide 1 of 2

Scope within a block - Ex. 1 predict the output 1. void scope2(void) //function header 2. {double v = 5.5; 3. int k, j; 4. cout << "v outside block = " << v<<'\n'; 5. for (k=1; k<=3; k++) 6. { int v = 17; // initialized in function 7. for (j=1; j<=2; j++) 8. {v++; 9. cout << "v inside block = " << v<<'\n'; 10. } 11. } 12. cout << "v outside block = " << v<<'\n'; 13. } slide 2 of 2

Scope within a block - Ex. 2 void scope2(void);// function prototype void main(void) int v=100; {int v=100; cout <<"v BEFORE function = "<<v<<'\n'; scope2(); cout <<"v AFTER function = "<<v<<'\n'; } slide 1 of 2

Scope within a block - Ex. 2 slide 2 of 2 1. void scope2(void) //function header 2. { double v = 5.5; 3. int k, j; 4. cout << "v outside block = " << v <<'\n'; 5. for (k=1; k<=3; k++) int v = { int v = 17; // initialized in function 7. for (j=1; j<=2; j++) v 8. { v ++; v 9. cout << "v inside block = " << v <<'\n'; 10. } 11. } 12. cout << "v outside block = " << v <<'\n'; }

Scope within a block OUTPUT 100BEFORE 5.5outside 18inside 19inside 18inside 19inside 18inside 19inside 5.5 outside 100AFTER j loops } } } * } k loop

Global Resolution Operator :: :: double rougon = ;// global void main(void) { double rougon = 12.3;// local cout<< rougon << “ = rougon, local\n” cout<< ::rougon << “ = rougon, global\n”; } OUTPUT OUTPUT 12.3 = rougon, local = rougon, global *

Variable Storage Classes Local auto static register  while (  ) {int k = 1; k++;  } * * * while (  ) {static int k = 1; k++;  }

Global static extern  Variable Storage Classes

Scope & Storage Classes - an example int x = 1; // global variable main() { int x = 5; // local variable to main cout << "local x in outer scope of main is " << x << endl; { // start new scope int x = 7; cout << "local x in inner scope of main is " <<x<< endl; } // end new scope cout << "local x in outer scope of main is " << x << endl;

Scope & Storage Classes - an example (continued) a(); // a has automatic local x b(); // b has static local x c(); // c uses global x a(); // a reinitializes automatic local x b(); // static local x retains its previous value c(); // global x also retains its value cout << "local x in main is " << x << endl; return 0; }// end of main()

Scope & Storage Classes - an example void a(void) { int x = 25; // initialized each time a is called cout << endl << "local x in a is " << x << " after entering a" << endl; ++x; cout << "local x in a is " << x << " before exiting a" << endl; }

Scope & Storage Classes - an example void b(void) { static int x = 50; // Static initialization only // first time b is called cout << endl << "local static x is " << x << " on entering b" << endl; ++x; cout << "local static x is " << x << " on exiting b" << endl; }

Scope & Storage Classes - an example void c(void) { cout << endl << "global x is " << x << " on entering c" << endl; x *= 10; cout << "global x is " << x << " on exiting c" << endl; }

Scope & Storage Classes - an example a(); // a has automatic local x b(); // b has static local x c(); // c uses global x a(); // a reinitializes automatic local x b(); // static local x retains its previous value c(); // global x also retains its value a(); b(); c(); *

Scope & Storage Classes - an example OUTPUT local x in outer scope of main is 5 local x in inner scope of main is 7 local x in outer scope of main is 5 local x in a is 25 after entering a local x in a is 26 before exiting a local static x is 50 on entering b local static x is 51 on exiting b global x is 1 on entering c global x is 10 on exiting c

Scope & Storage Classes - an example local x in a is 25 after entering a local x in a is 26 before exiting a local static x is 51 on entering b local static x is 52 on exiting b global x is 10 on entering c global x is 100 on exiting c local x in main is 5

Scope & Storage Classes - an example void a(void) { int x = 25; // initialized each time a is called cout << endl << "local x in a is " << x << " after entering a" << endl; ++x; cout << "local x in a is " << x << " before exiting a" << endl; } << ‘\t’ << ::x << ‘\t’ << ::x << endl; *

Common Errors 4 Passing incorrect data types 4 Using the same variable name for different variables ex. local - in both the calling and called functions global - must use ::

Common Errors 4 Wrong positioning of the called function prototype 4 Terminating a function header with a ; 4 Forgetting the data type of a function’s parameter

Debugging char = junk; and cin << junk; Prevention - plan first! Valuation tables Display values Use Find or Replace for == vs. = C++ Debugger

“Heavier-than-air flying machines are impossible.” Lord Kelvin, President of the Royal Society, 1895 End Note 1

“If A = success, then the formula is A = X + Y + Z. X is work. Y is play. Z is keep your mouth shut.” Albert Einstein End Note 2