Functions Scope local global Global Resolution Operator part II Data Flow Scope local global 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 pass data into a function /* in */ pass data out of a function /* out */ pass data into and out of a function /* inout */

Parameter and Data Flow 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 & out & 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); } *

Parameter and Data Flow Flow Out void media( /* out */ float& delta, /* out */ float& epsilon ) { delta = 1.0; epsilon = 0.0002; } inout epsilon = epsilon - 0.0001; epsilon = epsilon - 0.0001; *

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

Data Flow - Example #include<iostream.h> void getTemp(double&); void activity(double); void convertCtoF(double&); void main(void) { double temperature; getTemp(temperature); activity(temperature); }

Data Flow - Example out inout * * 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; inout * *

Data Flow - Example in * 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 flow parameter-passing for a parameter mechanism incoming pass-by-value outgoing pass-by-reference incoming/outgoing pass-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 { << yellow << ‘\n’; } 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 << ‘ ‘ }

I/O Example { << green << ‘\n’; } 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 <<‘ ‘ B5 return (yellow + 1); }

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

I/O Example The lines are executed in this order. 1 2 3 4 5 B B1 - B5 6 M M1 - M6 7 8 M M1 - M6 9 10 M B B1 - B5 M1 - M6 11 * * * *

I/O Example Mix memory Main green red blue yellow purple

Main Mix Blend * enter Blend 3 6 leave Blend 3 6 enter Mix 5 10 leave Mix 15 25 15 10 enter Mix 15 25 leave Mix 40 65 40 10 enter Blend 10 40 leave Blend 10 40 enter Mix 40 51 leave Mix 91 142 91 10 *

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 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; // 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 - ReadValues void main(void) { int a, b, c; float avg; 1. 2. 3. 4. 5. 6. 7. 8. 9. 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 - 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 - ReadValues * * void ReadValues( /* */ int& x, /* */ int& y, /* */ int& z ) { void ReadOne( char, int& ); ReadOne('1', x ); ReadOne('2', y ); ReadOne('3', z ); return; } out out * *

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

Example - Adjust * * void Adjust( /* */ int& i, /* */ int& j, inout /* */ 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 inout * *

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

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 in * *

Main ReadValues Adjust Average WriteResults ReadOne Enter value 1: 23 Adjusted values: 0, 33, 55 Sum: 88 Average: 29.3333

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: 5 y: 10 3. Swap-before swap: x: 5 y: 10 4. Swap-after swap: x: 10 y: 5 2. Main-after swap: x: 5 y: 10

Scope within a Block void Block1(int, char &); void Block2( ); int a1; // global char a2; // global int main() { . . . } 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 } . . . void Block2() { int a1; // prevents access to global a1 int b1; // local to Block2 while (…) { // Block3 int c1; // local to Block3 int b2; // prevents non-local access } // to b2 in Block1 . . . slide 2 of 2 *

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

Scope within a block - Ex. 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++) 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'; } slide 2 of 2

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

Global Resolution Operator :: double rougon = 999.99; // global void main(void) { double rougon = 12.3; // local cout<< rougon << “ = rougon, local\n” cout<< ::rougon << “ = rougon, global\n”; } OUTPUT 12.3 = rougon, local 999.99 = rougon, global * *

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

Variable Storage Classes Global static extern ý

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 from Deitel & Deitel 1e, fig 3.12

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() from Deitel & Deitel 1e, fig 3.12

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; } from Deitel & Deitel 1e, fig 3.12

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; } from Deitel & Deitel 1e, fig 3.12

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; } from Deitel & Deitel 1e, fig 3.12

Scope & Storage Classes - an example b(); c(); 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 from Deitel & Deitel 1e, fig 3.12 *

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 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 from Deitel & Deitel 1e, fig 3.12

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 from Deitel & Deitel 1e, fig 3.12

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; } from Deitel & Deitel 1e, fig 3.12 << ‘\t’ << ::x << endl; *

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

Common Errors Wrong positioning of the called function prototype Terminating a function header with a ; 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, End Note 1 “Heavier-than-air flying machines are impossible.” Lord Kelvin, President of the Royal Society, 1895

End Note 2 “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