Function. Introduction Library function New defined function Random number generator Scope Inline function Function overload Function Function

Function

IntroductionLibrary functionNew defined functionRandom number generatorScopeInline functionFunction overload

FunctionFunction

Why do we need function? Reuse and simplify a large program.

Chapter 7 and Chapter 8 (p309-p436)

IntroductionIntroduction

Library functionLibrary function1 // using library function.

2 #include <iostream>

3 #include <iomanip>

4 5 using namespace std;;

6 7 int main()

8 {9 cout << setw(4) <<123 << endl;

10 11 return 0; // indicates successful termination

12 13 } // end main

14

123

Include the header file Functions called by writing

setw (4);

4 can be replaced by Constants: setw( 5 ); Variables:

X=4; setw(x);

Expressions: X=2; setw( 6-x );

9 int x=4;10 cout << setw(x) <<123 << endl;

9 int x=2;10 cout << setw(6-x) <<123 << endl;

10 cout << setw(5) <<123 << endl;

Math library function Perform common mathematical calculations Include the header file <cmath> Example

cout << sqrt( 900.0 ); sqrt (square root) function The preceding statement would print 30

Method Description Example ceil( x ) rounds x to the smallest integer

not less than x ceil( 9.2 ) is 10.0 ceil( -9.8 ) is -9.0

cos( x ) trigonometric cosine of x (x in radians)

cos( 0.0 ) is 1.0

exp( x ) exponential function ex exp( 1.0 ) is 2.71828 exp( 2.0 ) is 7.38906

fabs( x ) absolute value of x fabs( 5.1 ) is 5.1 fabs( 0.0 ) is 0.0 fabs( -8.76 ) is 8.76

floor( x ) rounds x to the largest integer not greater than x

floor( 9.2 ) is 9.0 floor( -9.8 ) is -10.0

fmod( x, y ) remainder of x/y as a floating-point number

fmod( 13.657, 2.333 ) is 1.992

log( x ) natural logarithm of x (base e) log( 2.718282 ) is 1.0 log( 7.389056 ) is 2.0

log10( x ) logarithm of x (base 10) log10( 10.0 ) is 1.0 log10( 100.0 ) is 2.0

pow( x, y ) x raised to power y (xy) pow( 2, 7 ) is 128 pow( 9, .5 ) is 3

sin( x ) trigonometric sine of x (x in radians)

sin( 0.0 ) is 0

sqrt( x ) square root of x sqrt( 900.0 ) is 30.0 sqrt( 9.0 ) is 3.0

tan( x ) trigonometric tangent of x (x in radians)

tan( 0.0 ) is 0

Math library functions.

1 // using math library function.


3 #include <cmath>

4 5 using std::cout;

6 using std::endl;

7 8 int main()

9 {10 // loop 10 times and calculate and output

11 // square root of x each time

12 for ( int x = -5; x <= 5; x++ )

13 cout << abs (x) << “, "; // function call

14 15 cout << endl;

16 17 return 0; // indicates successful termination 18 } // end main

Parentheses () cause function to be called. When the call done, the function result will be provided.

Head file.

5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 5,

1 // using math library function.


3 // do not need any other header file.


6 using std::endl;

7 8 int main()


11 // square root of x each time

12 for ( int x = -5; x <= 5; x++ ) {

13 If ( x <0) cout << -x << “, "; // if else, implementation of abs (x)

14 else cout << x << “, ";

15 }16 cout << endl;


Without function call, the program needs implementation of abs here.

5, 4, 3, 2, 1, 0, 1, 2, 3, 4, 5,

Thinking?In program 1:

Does the function know when it will be called?Is that function reused 11 times in the loop? (Does the name abs appear 11 times?)Do you care how to get absolute number in main?

Comparing with a main program providing a detailed implementation of abs inside that loop, is this main more simple and easier to develop?

No

YesNo

Yes

12 for ( int x = -5; x <= 5; x++ ) {

13 If ( x <0) cout << -x << “, ";

14 else cout << x << “, ";

15 }

12 for ( int x = -5; x <= 5; x++ )

13 cout << abs (x) << “, ";

Program 1 Program 2

New defined functionNew defined function 3 aspects

Function prototype Function call Function definition

Argument and parameter Pre-condition and post-condition Reference parameter Return value How to solve real problems by using

arguments and parameters.

3 aspects3 aspectsFunction prototype

Is used by compiler to check if the function call matches the function definition.

A simple sample:void function-name( );

Calling/invoking a function (function call) A simple call:

function-name(); Parentheses are used to call function (Control

goes to function). When the call done, the program will return to

the point from which the function was called (Control goes back to caller).

3 aspects3 aspectsFunction definition

A simple function definition

void function-name(){ statements}

Simple sample

Function heading, without “;”.

******************************

******************************

Welcome!

******************************

******************************

3 aspects3 aspectsFunction definition

A simple function definition

void function-name(){ declarations and statements}

1 // using new defined function.


3 using namespace std;

4 void print_star_one_line ( ); 56 int main()

7 {8 print_star_one_line ( ); // print one line of stars.

9 print_star_one_line ( ); // another line

10 cout <<“Welcome!“<<endl;

11 print_star_one_line ( ); // print two lines of stars.

12 print_star_one_line ( );


16 17 void print_star_one_line ( )

18 {19 cout << “******************************“<< endl;

20 } // end of function

Parentheses () cause function to be called in main(). When the function done, the program will do the next statement.

Function prototype.

Function definition. Its statements inside will be executed when the function is called.

A function cannot be defined in other function such like:

17 void print_star_one_line ( )

18 {19 void print_one_star ( )

20 {21 cout << ”*” << end; 22 } // end of function print_one_star

......

.. } // end of function print_star_one_line

******************************

AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA

Welcome!AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA ******************************

Thinking?Do we need two different functions?

Argument and parameterArgument and parameter Make function more general by input parameter. With parameter in the function definition, function

call with different value of argument can fulfill similar tasks.

Argument: A variable or expression listed in a function call; Also called actual argument or actual parameter.

Parameter: A variable declared in a function heading; Also called formal argument or formal parameter.

Argument and parameterArgument and parameter Example.

Express the following procedure: Two numbers; add them together; divide by 2. Try 9 and 8 Try 7 and 4

Did you use (x+y)/2 when you want to express the procedure?

Did you use (a+b)/2 when you want to express the procedure?

1 // using list of arguments and parameters, argument promotion.



4 void showavg ( int, int ); 56 int main()

7 {8 showavg (9, 8);

9 showavg (7, 4);

10 return 0; //successful termination 11 } // end main

12 13 void showavg (int num1, int num2)

14 {15 cout << float(num1 + num2)/2 <<endl;


We tried 9 and 8.

We tried 7 and 4

Instead of x and y (or a and b), I used num1 and num2.

Argument and parameterArgument and parameterGeneral format (Prototype, Call, and Definition)

Function prototypeTells compiler argument type. void function-name( Datatype );

Function call function-name( argument );An argument is passed to parameter in function definition

Function definitionvoid function-name( DataType VariableName ){ statements // use VariableName; its value = value of the argument.

}

1 // using argument and parameter.



4 void print_one_line ( char ); 56 int main()

7 {8 print_one_line (‘*’ ); // print one line of stars.

9 print_one_line (‘A’ ); // print one line of ‘A’s.


11 print_one_line (‘A’ ); // print another line of ‘A’s.

12 print_one_line (‘*’ ); // print another line of stars.


16 17 void print_one_line ( char ch )

18 {19 Int i;

20 for ( int x = 1; x <= 30; x++ )

21 cout << ch;

22 cout << endl;


‘*’ is passed to parameter.

Use parameter ch as a variable. Its value comes from the argument.

ch

main Print_one_line

‘*’

ch‘A’

Sequence Diagram

******************************


Welcome!AAAAAAAAAAAAAAAAAAAAAAAAAAAAAA ******************************

Argument and parameterArgument and parameterThe value of argument and parameter

Arguments can be constants, variables, and expressions

The argument will be evaluated to match the parameter when the function is called.

Force arguments to be of definition typecout << sqrt(4) //Converting 4 to double (4.0)

The value will be passed to parameter. The parameter is a variable and its value is

according to the argument in different call.




4 void print_one_line (char ); 56 int main()

7 {8 char c=’A’;

9 print_one_line (‘*’ ); // one line ‘*’.

10 print_one_line (c ); // one line ‘A’.


12 print_one_line (c+ ’d’- ’c’ ); //one line ‘B’.

13 print_one_line (‘*’ ); // print another line of ‘*’.

14 return 0; // indicates successful termination 15 } // end main


18 {19 int i;

20 for ( int x = 1; x <= 30; x++ )

21 cout << ch;

22 cout << endl;


Constants, ‘*’ is passed to parameter, one line ‘*’.

Variable, its value ‘A’ is passed to parameter, one line ‘A’.

Expression, its value ‘B’ is evaluated and passed to parameter, one line ‘B’.

ch

main Print_one_line

‘*’

ch‘A’

Sequence Diagram

ch‘B’

constant value

value of variable c

value of expression

******************************


Welcome!BBBBBBBBBBBBBBBBBBBBBBBBBBBBBB******************************

Argument and parameterArgument and parameterAdvanced format (Prototype, Call, and Definition

for multiple arguments and parameters) Function prototype

void function-name( DataTypeList );The name of the function followed by data types of

arguments. Comma separated list.

Function call function-name( ArgumentList );The arguments are passed to the parameters according to

their positions, left to right.Comma separated list of arguments.

Argument and parameterArgument and parameterAdvanced format (Prototype, Call, and Definition)

Function definitionvoid function-name( ParameterList ){ statements}

If the list is present, it has the following form: DataType Parameter1, DataType Parameter2, …

Comma separated list.

1 // using list of arguments and parameters, argument promotion.




7 {8 char c=’a’;

9 int i=9, j=2;

10 showavg (i, j);

11 showavg (i, 2.5);

12 showavg (c*300, 11);





Argument List. The value of i and j, 9 and 2, are passed to num1 and num2.

Datatype List.

5.5

5.5

14555.5

The value of 2.5 (float) will be truncated to 2 and be passed to num2 (int).

Parameter List.

The type of c*300 will be promoted to int because it’s char * int.

Real Case Real Case ((A company and its delivery)

Thinking? For a guy who delivers the product of that company:

Does he know what his job is? (function definition) Does he know what he will deliver? (parameter)

For the company: Does the company knows what the guy will deliver? (argument) Does the company care how he will deliver? (Does the main include

the implementation of its functions?) Does the company need confirm the delivery? (Control goes back to

main or caller when the function is done.)

Company Guy of delivery service

Product = ‘*’His job is to handle (deliver) this ٱ.Control goes back

(delivery confirmation).

‘*’

Call delivery service

Pre-condition and post-conditionPre-condition and post-conditionPre-condition:

To ensure there is no misuse. An assertion that must be true before the function call It may include:

The acceptable range of argument The external resources the function used and their status.

Post-condition: To ensure the expecting result. An assertion that should be true after the function is called. It may include:

The results All the external things this execution can change.

1 // Function void showavg (int, int).

2 // Pre-condition:

3 // Argument: two integer numbers

4 // external resource: None

5 // Post-condition:

6 // result: show the average on screen

7 // external thing changed: Only the monitor.




void my_function ( ); //function prototype

int main( ){ my_function( ); //function call

return 0;}

void my_function ( ) //function definition{

}

int

k

int x

int k=3, m =4 ;

, int

, m

, int y

Reference parameterReference parameterValue parameter

A parameter that receives a copy of the value of the corresponding argument.

The change of value of this parameter variable in the function won’t change any thing in its caller (main).

ch

main function

‘*’

ch‘A’

Sequence Diagram

ch‘B’

constant value

value of variable c

value of expression

‘*’

‘A’

‘B’





7 {8 char c=’A’;

9 print_one_line (‘*’ );

10 print_one_line (c );


12 print_one_line (c+ ’d’- ’c’ );


14 return 0;

15 } // end main


18 {19 int i;

20 for ( int x = 1; x <= 30; x++ )

21 cout << ch;

22 cout << endl;


Reference parameterReference parameter A parameter that receives the location of the caller’s

argument (main). The change of value of this parameter variable in the

function will bring the change to main after the function call.

The argument of its function call should be a variable (declared in main).

General format:void function-name( Datatype & ); //prototype

function-name( ArgumentVariable ); //call void function-name( DataType & VariableName )

// definition

ch, i

main Function (char & ch)

‘*’

ch = ‘A’;

Sequence Diagram

variable i

Function ( i )

‘*’

‘A’‘A’

1 // using reference parameter.



4 void showavg ( int, int, float & ); 5 int main()

6 {7 float cf=1.2;

8 int i=9, j=2;

9 showavg (i, j,cf);

10 cout <<i << endl << cf <<endl 11 return 0; //successful termination 12 } // end main

13 14 void showavg (int num1, int num2 , float & avg)

15 {16 avg = float(num1 + num2)/2;

17 num1 = 2;


A variable in main. It will be used as reference argument.

Datatype &

9

5.5

Function call. No & here.

The change of value of reference parameter. This change in function is brought to main by reference parameter.

The change of value of value parameter won’t change

the value of the argument variable i in main.

num1

main showavg

9 2

num2

Sequence Diagram

avg, cf

cf

1. 2

9 2 1.2

num1 num2 avg, cf

2 2 5.5cf

5.5

i j

9 2

i j

ReturnReturn Return results by using reference parameters Return result by using return statement in function

Function prototype Tells compiler return type

int square( int ); Function takes an int and returns an int

Function call

cout << square(x); After finished, passes back result

ReturnReturn Return result by using return statement in function

Function definition

return-value-type function-name( parameter-list ){ statements

return Result;}

Return-value-type: Data type of result returned (use void if nothing returned)

The value of Result will be evaluated and passed back to caller (main).

If no data to return (void), use return;

1 2 // using return statement.



6 using std::endl;

7 8 int square( int ); // function prototype

9 10 int main()


13 // square of x each time

14 for ( int x = 2; x <= 10; x++ )

15 cout << square( x ) << " "; // function call

16 17 cout << endl;


20 21 } // end main

22

Parentheses () cause function to be called. When done, it returns the result.

Function prototype: specifies data types of arguments and return values. square expects int, and returns an int.

23 // square function definition returns square of an integer

24 int square( int y ) // y is a copy of argument to function

25 { 26 return y * y; // returns square of y as an int

27 28 } // end function square

4 9 16 25 36 49 64 81 100

Definition of square. Returns y * y, or y squared.

1 2 // using reference parameters for several return values.



6 using std::endl;

7 8 void square_and_root( int, int&, float& ); // function prototype

9 10 int main()

11 {12 int s;

13 float r;

14 for ( int x = 2; x <= 5; x++ ) {

15 square_and_root( x, s, r ) ; // function call

16 cout << s << “, " << r << “; "; // show two results

17 }18 cout << endl; 19 return 0; // indicates successful termination

20 21 } // end main

22

Parentheses () cause function to be called. When done, it returns two results in variables s and r.

Function prototype: specifies data types of arguments and return values. Square_and_root expects an int, and returns two results in reference parameters int & and float &.

23 // function definition returns square and square root

24 void square_and_root( int x, int &y, float & z )

25 { 26 y = x* x; // returns square of x as an int

27 z = sqrt(x); // returns square root of x as an float

28 } // end function square

4, 1.4121; 9, 1.73205; 16, 2; 25, 2.23607;

Definition of square. Returns the change of y and z to main by using reference parameter.

24 int square( int y )

25 {

26 return y * y;

27

28 }

24 void square_and_root( int x, int &y, float & z )

25 { 26 y = x* x;

27 z = sqrt(x);

28 }

The function using return statement is easy to read and can return one value to its caller.The function using reference parameter

has a long list of parameters.has a complicated execution.can return more values.

Exercises



345 int main()

6 {7 for ( int x = 1; x <= 30; x++ )

8 cout << ”*”;

9 cout << endl;

10 for ( int x = 1; x <= 30; x++ )

11 cout << ”*”;

12 cout << endl;


14 for ( int x = 1; x <= 30; x++ )

15 cout << ”*”;

16 cout << endl;

17 for ( int x = 1; x <= 30; x++ )

18 cout << ”*”;

19 cout << endl;

20 21 return 0;

22 }



3 void print_one_line ( ); 45 int main()

6 {7 print_one_line ( );

8 print_one_line ( );




12 return 0;

13 } // end main

14 15 void print_one_line ( ) // function heading

16 { // function body

17 for ( int x = 1; x <= 30; x++ )

18 cout << ”*”;

19 cout << endl;


Function prototype

Function call

Function definition

******************************

******************************

Welcome!

******************************

******************************

******************************


Welcome!BBBBBBBBBBBBBBBBBBBBBBBBBBBBBB******************************





7 {8 char c=’A’;


10 print_one_line (c );


12 print_one_line (c+ ’d’- ’c’ );


14 return 0;

15 } // end main


18 {19 for ( int x = 1; x <= 30; x++ )

20 cout << ch;

21 cout << endl;


Type of argument

Argument

Parameter

Question on page 19: Get the average of two numbers

Two factors: (x+y) /2 (or (a+b)/2)Two argumentsTwo parameter variables

How to solve real problems by using arguments and parameters

1 //using multiple arguments and parameters.




7 {8 showavg (9, 8);

9 showavg (7, 4);





The average number is printed out when the function is called every time.How can the caller use the result of function?

1 // using return statement.



4 float get_avg ( int, int ); 56 int main()

7 {8 cout << get_avg (9, 8) <<endl;

9 cout << get_avg (7, 4) <<endl;


12 13 float get_avg (int num1, int num2)

14 {15 return float(num1 + num2)/2;


Do we need return? Program using return statement

Return statement

Return type




4 void get_avg ( int, int, float & ); 56 int main()

7 {8 int r;

9 get_avg (9, 8, r );

10 cout << r <<endl;

11 get_avg (7, 4, r );

12 cout << r <<endl;


15 16 void get_avg (int num1, int num2, float & res)

17 {18 res = float(num1 + num2)/2;


Program using reference parameter

Reference parameter

Solution for exercises Get the larger one of two numbers Two factors Two arguments Two parameter variables




4 int get_larger ( int, int ); 56 int main()

7 {8 int x, y;

9 cin >> x >> y;

10 cout << get_larger (x, y) <<endl; //function call 11 return 0; //successful termination 12 } // end main

13 14 int get_larger (int num1, int num2)

15 {16 if (num1 > num2)

17 return num1;

18 else return num2;


“cout <<___ ; //function call” -> function with return statement




4 int get_larger ( int, int ); 56 int main()

7 {8 int x, y;

9 cin >> x >> y;

10 cout << get_larger (x, y) <<endl;


13 14 int get_larger (int num1, int num2)

15 {16 return (num1 > num2)? num1: num2;


1 // using reference parameter.



4 void get_larger ( int, int, int & ); 56 int main()

7 {8 int x, y, larger;

9 cin >> x >> y;

10 get_larger (x, y, larger );

11 cout << larger <<endl;


14 15 void get_avg (int num1, int num2, int & res)

16 {17 res = (num1 > num2)? num1: num2;


“cout <<larger;” -> function with reference parameter “larger”.

UsageFormatExample

Random number generatorRandom number generator

Random selection rolling dice, and etc.

rand function (<cstdlib>) i = rand(); Generates unsigned integer between 0 and RAND_MAX

(usually 32767) Generates integer between a and b.

i = rand() % 6 + 1; “Rand() % 6” generates a number between 0 and 5 (scaling) x % y is between 0 and y – 1, i.e., 10 % 3 is 1 “+ 1” makes the range 1 to 6 (shift)

Example: Program to roll dice.

1 // Shifted, scaled integers produced by 1 + rand() % 6.



4 #include <cstdlib> // contains function prototype for rand

5 6 using namespace std;

7 8 int main()

9 {10 // loop 20 times

11 for ( int counter = 1; counter <= 20; counter++ ) {

12 13 // pick random number from 1 to 6 and output it

14 cout << setw( 10 ) << ( 1 + rand() % 6 ); 15 // if counter divisible by 5, begin new line of output

16 if ( counter % 5 == 0 )

17 cout << endl;

18 19 } // end for structure


22 } // end main

Output of rand() scaled and shifted to be a number between 1 and 6.

Head file.

6 6 5 5 6

5 1 1 5 3

6 6 2 4 2

6 2 3 4 1

Thinking

Is this fair?

1 // Roll a six-sided die 6000 times.




5 6 using namespace std;

7 8 int main()

9 {10 int frequency1 = 0;

11 int frequency2 = 0;





16 int face; // represents one roll of the die

17

18 // loop 6000 times and summarize results

19 for ( int roll = 1; roll <= 6000; roll++ ) {

20 face = 1 + rand() % 6; // random number from 1 to 6

21 22 // determine face value and increment appropriate counter

23 switch ( face ) {

24 case 1: // rolled 1

25 ++frequency1;

26 break;


28 ++frequency2;

29 break;


31 ++frequency3;

32 break;


34 ++frequency4;

35 break;


37 ++frequency5;

38 break;


40 ++frequency6;

41 break;

42 default: // invalid value

43 cout << "Program should never get here!";

44 45 } // end switch

46 47 } // end for

48 49 // display results in tabular format

50 cout << "Face" << setw( 13 ) << "Frequency"

51 << "\n 1" << setw( 13 ) << frequency1

52 << "\n 2" << setw( 13 ) << frequency2

53 << "\n 3" << setw( 13 ) << frequency3

54 << "\n 4" << setw( 13 ) << frequency4

55 << "\n 5" << setw( 13 ) << frequency5

56 << "\n 6" << setw( 13 ) << frequency6 << endl;


59 60 } // end main

Default case included even though it should never be reached. This is a matter of good coding style

Face Frequency

1 1003

2 1017

3 983

4 994

5 1004

6 999

Calling rand() repeatedly Gives the same sequence of numbers To get different random sequences

Provide a seed value• Like a random starting point in the sequence• The same seed will give the same sequence

srand(seed); • <cstdlib>• Used before rand() to set the seed

1 // Randomizing die-rolling program.



4 #include <cstdlib>


6 7 int main()

8 {9 unsigned seed;

10 11 cout << "Enter seed: ";

12 cin >> seed;

13 srand( seed ); // seed random number generator

14 // loop 10 times


16 // pick random number from 1 to 6 and output it

17 cout << setw( 10 ) << ( 1 + rand() % 6 );

18 // if counter divisible by 5, begin new line of output

19 if ( counter % 5 == 0 )

20 cout << endl;

21 } // end for

22 return 0; // indicates successful termination

23 } // end main

Setting the seed with srand() before rand().

Enter seed: 67

6 1 4 6 2

1 6 1 6 4

Enter seed: 432

4 6 3 1 6

3 1 5 4 2

Enter seed: 67

6 1 4 6 2

1 6 1 6 4

rand() gives the same sequence if it has the same initial seed.

Can use the current time to set the seed Use current time as seedsrand( time( 0 ) );time( 0 );

• <ctime>• Returns current time in seconds

Number = shiftingValue + rand() % scalingFactor

• shiftingValue = first number in desired range• scalingFactor = width of desired range

1 // Shifted, scaled integers produced by 1 + rand() % 6.




5 #include <ctime> // contains function prototype for time


7 8 int main()

9 {10 srand ( time( 0 ));


12 13 // pick random number from 1 to 6 and output it

14 cout << setw( 10 ) << ( 1 + rand() % 6 ); 15 // if counter divisible by 5, begin new line of output

16 if ( counter % 5 == 0 )

17 cout << endl;

18 19 } // end for structure


22 } // end main

Use current time as seed.

1 1 1 3 3

1 4 5 6 6

5 2 3 6 1

1 5 6 3 3

1 5 2 1 4

2 2 3 5 2

4 6 1 3 5

5 5 6 5 2

IntroductionLocal scopeGlobal scopeName precedenceStatic variable

ScopeScope

num1

main

showavg

9 2

cf

1. 2

cf

5.5

i j

avg

Lifetime

num2

5.5

Introduction (Lifetime)Introduction (Lifetime)

9 2

5 int main()

6 {7 float cf=1.2;

8 int i=9, j=2;

9 showavg (i, j,cf);

10 cout <<i << endl << cf <<endl 11 return 0; //successful termination 12 } // end main



17 num1 = 2;


Introduction (scope)Introduction (scope)Scope

Portion of program where identifier can be used.

Local scopeGlobal scope

Local scopeLocal scopeLocal variables, function parametersScope begins at declaration, ends at right

braceVariable created when program enters its

blockVariable invalid when program leaves blockVariable destroyed when program reaches

the right brace of this block

1 // using arguments and parameters.



4 void showavg ( int, int, float & ); 5 int main()

6 {7 float cf=1.2;

8 int j;

9 for ( j = 1; j <= 5; j++ ) {

10 int i = 9;

11 showavg( i, j, cf ) ; // function call

12 cout <<i << endl << cf <<endl 13 }14 return 0; //successful termination 15 } // end main




num1

i

Local scope starts from declaration

Local variable will be invalid when the program leaves main for showavg.

Create a new block, giving i block scope. When the block ends (the program reaches the right brace of the block), this i is destroyed.

{

…………

int i;i=i+1;…………

}

{int i;…………

i=i+1;…………

}

int i;i = i+2;

Global scopeGlobal scopeGlobal variables (constants), function

definitions and prototypesDefined outside of any function in a fileScope begins at declaration, ends at the

end of this fileVariable created when program startsVariable is valid from its declaration to the

end of this file.Variable destroyed when program ends

1 // using global variables.



4 5 double c_area( int );

6 const double pi = 3.14;

7 8 int main()

9 {10 cout << “When pi is " << pi <<endl;

1112 for ( int x = 1; x <= 10; x++ )

13 cout << c_area( x ) << " ";

14 cout << endl;

15 return 0;

16 } // end main

17 18 double c_area( int radius)

19 {

20 return radius * radius * pi;


1 // using global variables.



4 5 const double pi = 3.14;

67 double c_area( int radius)

8 { 9 return radius * radius * pi;


11 12 int main()


1516 for ( int x = 1; x <= 10; x++ )

17 cout << c_area( x ) << " ";

18 cout << endl;

19 return 0;

20 } // end main

21

Thinking

Local GlobalWhen is it created?When is it destoried?

Is it still valid when thecontrol goes out of the local block?

- - End of local End of fileblock

No Yes

Name precedenceName precedenceWhen a function declares a local identifier

with the same name as a global identifier, the local identifier takes precedence within the function.

The precedence that a local identifier in a function has over a global identifier with the same name in any references that the function makes to that identifier; also called name hiding.

1 // using name precedence.



4 5 double c_area( int );

6 const double pi = 3.14;

7 8 int main()


1113 cout << c_area(10 ) << " ";

14 cout << endl;

15 return 0;

16 } // end main

17 18 double c_area( int radius)

19 {

20 int pi = 3;

20 return radius * radius * pi;


pi

3.14

pi

3

main

c_area

When pi is 3.14

300

Static variableStatic variableVariables exist for entire programStatic local variables in function

Keeps value between function calls Variable created once when program first

entered the function Only known in own function Variable destroyed when program ends

1 // using local static.



4 void useStaticLocal( )

5 6 int main()

7 {8 for ( int x = 1; x <= 10; x++ )

9 useLocal( );

10 return 0;

11 } // end main

12 13 void useLocal ( )

14 {15 // initialized only first time useStaticLocal is called

16 int y = 50;

17 18 cout << "local x is " << y ++ << endl;

19 } // end function useStaticLocal Local variable of function; it is initialized every time when the program call this function.

Y=50

main

useLocal

51

Y=50

useLocal

51

Y=50

useLocal

51

…

local x is 50

local x is 50

local x is 50

local x is 50

local x is 50

local x is 50

local x is 50

local x is 50

local x is 50

local x is 50

1 // using local static.



4 void useStaticLocal( )

5 6 int main()

7 {8 for ( int x = 1; x <= 10; x++ )

9 useStaticLocal( );

10 return 0;

11 } // end main

12 13 void useStaticLocal ( )

14 {15 // initialized only first time useStaticLocal is called

16 static int y = 50;

17 18 cout << "local static x is " << y ++ << endl;

19 } // end function useStaticLocal Static local variable of function; it is initialized only once, and retains its value between function calls.

Y=50

main

useStaticLocal

51

useStaticLocal

52

useStaticLocal

53

…

local static x is 50










Inline functionInline functionInline functions

Keyword inline before function Asks the compiler to copy code into program

instead of making function call Reduce function-call overhead Compiler can ignore inline

Good for small, often-used functions

Exampleinline double cube( const double s )

{ return s * s * s; }

const tells compiler that function does not modify s

1 // Using an inline function to calculate.



4 5 // Definition of inline function cube. Definition of function

6 // appears before function is called, so a function prototype

7 // is not required. First line of function definition acts as

8 // the prototype.

9 inline double cube( const double side )

10 { 11 return side * side * side; // calculate cube

12 } // end function cube

13 14 int main()

15 {16 double sideValue;

17 cout << "Enter the side length of your cube: ";

18 cin >> sideValue;

19 // calculate cube of sideValue and display result

20 cout << "Volume of cube with side "

21 << sideValue << " is " << cube( sideValue ) << endl;


23 } // end main

Enter the side length of your cube: 3.5

Volume of cube with side 3.5 is 42.875

Function overloadingFunction overloadingFunction overloading

Functions with same name and different parameters More general, should perform similar tasks

I.e., function to square ints and function to square floats

int square( int x) {return x * x;}

float square(float x) { return x * x; }

Overloaded functions distinguished by signature Based on name and parameter types (order matters)

1 // Using function overloading to calculate.



4 5 inline double square ( const double side )

6 { 7 cout << “double “;

8 return side * side; // calculate double square


10 11 inline int square ( const int side )

12 {

13 cout << “integer “;

14 return side * side; // calculate int square


16 17 int main()

18 {19 // calculate squre of sideValue and display result

20 cout << “Square with side 2 is " << square( 2 ) << endl;

21 cout << “Square with side 3.2 is " << square( 3.2 ) << endl;


23 } // end main

The proper function is called based upon the argument (int or double).

Square with side 2 is integer 4

Square with side 3.2 is double 10.24

1 // Fig. 3.4: fig03_04.cpp

2 // Finding the maximum of three floating-point numbers.



6 using std::cin;

7 using std::endl;

8 9 double maximum( double, double, double ); // function prototype

10 11 int main()

12 {13 double number1;

14 double number2;

15 double number3;

16 17 cout << "Enter three floating-point numbers: ";

18 cin >> number1 >> number2 >> number3;

19 20 // number1, number2 and number3 are arguments to

21 // the maximum function call

22 cout << "Maximum is: "

23 << maximum( number1, number2, number3 ) << endl;


Function maximum takes 3 arguments (all double) and returns a double.

26 27 } // end main

28 29 // function maximum definition;

30 // x, y and z are parameters

31 double maximum( double x, double y, double z )

32 { 33 double max = x; // assume x is largest

34 35 if ( y > max ) // if y is larger,

36 max = y; // assign y to max

37 38 if ( z > max ) // if z is larger,

39 max = z; // assign z to max

40 41 return max; // max is largest value

42 } // end function maximum

Enter three floating-point numbers: 99.32 37.3 27.1928Maximum is: 99.32



Comma separated list for multiple parameters.

Documents

Function. Introduction Library function New defined function Random number generator Scope Inline function Function overload Function Function