1. Functions Scope local global Global Resolution Operator part II
Data Flow
Scope local global
Global Resolution Operator part II

2. 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.

3. 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 */

4. 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)

5. 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’; } *

6. 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); } *

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

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

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

10. 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
* *

11. 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 *

12. Data Flow data flow parameter-passing for a parameter mechanism
incoming pass-by-value
outgoing pass-by-reference
incoming/outgoing pass-by-reference

13. 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'; }

14. 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 << ‘ ‘ }

15. 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); }

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

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

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

19. Main Mix Blend * enter Blend 3 6 leave Blend 3 6 enter Mix 5 10
leave Mix
15 10
enter Mix
leave Mix
40 10
enter Blend
leave Blend
enter Mix
leave Mix
91 10 *

20. 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.

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

22. 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.
* *

23. 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
* * * *

24. 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";

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

26. 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); }

27. 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
* * * *

28. 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
* *

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

30. 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
* *

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

32. 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
* *

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

34. 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';

35. 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

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

37. . . . . . . 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 *

38. 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

39. 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

40. 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

41. 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

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

43. 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 = rougon, local = rougon, global
* *

44. 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 }
* * *

45. Variable Storage Classes
Global static extern ý

46. 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

47. 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

48. 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

49. 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

50. 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

51. 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 *

52. 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

53. 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

54. 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; *

55. 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 ::

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

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

58. “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

59. 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