1. Functions
prototypes
arguments
overloading
return values part I

2. Functions
are self-contained blocks of code, the inner workings of which are invisible to the remainder of the program.
are subprograms in C++ .
perform a specific task.
can act on data and return a value.
Every C++ program has at least one function: main().
* * * *

3. Functions Why use functions?
make programs easier to write, debug and maintain - divide and conquer!
Two main types of functions:
predefined -- found in the header files
user-defined -- today’s topic *

4. Function - an example { int var1=1, var2=2, var3=3, var4=4;
function1(“ASU”, var1);
some statements;
function2(var4, var3);
function3(var2); }

5. Function - an example
void function1(char name, int place) { cout << name << “ is #” << place << endl; }
void function2(int al, int mel) { cout <<“var3 x var4 = “ << mel / al<<endl; }
void function3(int casey) { cout << casey << “ is the value in var2\n”; }

6. Function properties may be called may be passed data called arguments
may return a value to the calling program
will not change the data stored in a received variable unless specifically instructed to do so

7. Functions 1. #include <iostream.h> 2. void demofunction(void);
3. void main(void) { cout << "In main\n"; demofunction(); cout << "Back in main\n"; }
9. void demofunction(void) { cout << "In DemoFunction\n"; cout << “Still in function.\n”; }

8. Function Output Line # - 12.) Still in function. * * * * 5. In main
6. (calls function - 11.) In Demo Function
- 12.) Still in function.
7. Back in main
* * * *

9. Function declaration double Pythagorus( double, double );
data types only

10. Function Syntax Syntax { statements function body } *
function header line function header
{ statements function body } *

11. Function Header Syntax
type function_name(parameters) no ;
Example
double Pythagorus(double a, double b)

12. { Function Definition Example double Pythagorus(double a, double b) {
type var
Example double Pythagorus(double a, double b) {
double c;
c = sqrt(a*a + b*b);
return c; }
no ;
* *

13. Function Call void main(void) { cout << “The hypotenuse is “
<< Pythagorus(12, 5); }
OUTPUT
The hypotenuse is 13

14. Program Structure #include <iostream.h> function prototypes; {
void main(void) {
variable declarations; statements [including function calls] }
function definition(s)

15. Function Prototypes Syntax return type function_name(type);
Example double Pythagorus(double, double); *

16. Function Prototypes Examples void do_stuff(void);
double Pythagorus(double, double);
void do_stuff(void);
double times-em(int, int, int, int);
double myfunc(double, int);
void print_em(char, double);

17. Function Calls Syntax function_name(arguments);
Example Pythagorus(3.0, 4.0);
* *

18. Function Calls find_max(firstnum, secnum); memory find_max( , ) 865
9090
secnum
memory
get firstnum
get secnum
find_max( , )
find_max(firstnum, secnum);
865
9090
* * * * * *

19. Function Calls answer = Pythagorus(3.0,4.0);
cout << “The hypotenuse = “
<< answer << endl;
cout << “The hypotenuse = “ << Pythagorus(3.0,4.0)<<endl; *

20. Function Calls answer = Pythagorus(3.0,4.0); answer = answer * 100;
cout << “The hypotenuse = “
<< answer << endl;
cout << “Hypotenuse = “ << Pythagorus(3.0,4.0) * 100 <<endl; *

21. Program Structure #include <iostream.h> function prototypes; {
void main(void) {
variable declarations; statements [including function calls] }
function definition(s)

22. Program Structure #include <iostream.h> square prototype
main function square call
cube call
square function
cube function
#include <iostream.h>
square prototype
cube prototype

23. Program Structure . . . int square(int); // function prototype
int cube(int); // or function declaration
void main(void) {
int x = 8;
cout <<“The square is “<< square(x) <<‘\n’;
cout <<“The cube is “ << cube(x) <<endl;
. . . }
int square(int n) // function definition
{ continued on next slide

24. {OR return n*n; {OR return n*n*n; Program Structure
int square(int n) // function definition {
int answer;
answer = n*n;
return answer; }
int cube(int n) // function definition
answer = n*n*n;
{OR return n*n;
{OR return n*n*n; *

25. Function Summary Prototype type function_name(parameter types);
double Pythagorus(double, double);
Call
function_name(actual parameters);
Pythagorus(height, base);
Definition formal
type function_name(parameter types & names) { }
double Pythagorus(double a, double b)
* * * * *

26. Function Overloading
Two or more distinct functions may have the same name.
The data types of the arguments in the function calls must match those in the prototypes and in the definitions.
The same function is given multiple definitions or implementations. The correct one is chosen by the compiler, not the programmer.
* * *

27. Function Overloading
The functions must differ in their parameter lists. The type and/or number of parameters must be different.
Examples
double myFunction(int, int, int); int myFunction(double, int, int);
int myFunction (double, double);
void myFunction(double); *

28. { } Function Overloading . myFunction(3,4,5); myFunction(3.0, 4.0);
// a is used
// c is used
// b is used
// d is used
a double myFunction(int, int, int) b int myFunction(double, int, int)
c int myFunction (double, double)
d void myFunction(double) }
Header
* * * *

29. Returning Values A function can receive many values
Only one value can be directly returned

30. Returning Values The return statement:
tells the function which value to send back to the calling program
terminates the function call and returns immediately to the calling program

31. Return Statement Syntax return expression; Examples return c;
return hypotenuse;

32. Return Statement int find_max(int x, int y) { int maximum;
if (x >= y) maximum = x; else maximum = y;
return maximum; }
same data type *

33. Passing Data
passing by value gives a single value
passing by reference may give back several values accomplished by using references (this topic) using pointers *

34. Passing Data - by Value
passing by value: A copy of a value is passed from the calling function to the called function.
double Pythagorus(double a, double b) { double c;
c = sqrt(a*a + b*b);
return c; }
double Pythagorus(double a, double b) { a = a * a;
b = b * b;
double c = sqrt(a*a + b*b); return c; }
* *

35. Storing Values into Parameters
call to find_max
find_max(firstnum, secnum);
value in first_num is passed
value in sec_num is passed
find_max(x, y) x
865
9090 y
arguments
* *

36. Passing Data - by Value * * void main(void)
{ double height = 4.0, base = 3.0;
double Pythagorus(double, double);
cout << “Hypotenuse = “ << Pythagorus(height, base)<<endl;
. . . }
double Pythagorus(double a, double b)
{ double c; c = sqrt(a*a + b*b);
return c;
4.0
3.0
* *

37. Passing Data - by Value * double Pythagorus(double a, double b)
4.0
3.0
double Pythagorus(double a, double b)
{ double c;
a++;
b++;
c = sqrt(a*a + b*b);
return c; }
back in main: cout << height;
cout << base: *

38. Passing Data - by Value void print_val(int); // function prototype
void main(void)
{ int w = 3;
cout <<"w before the function call is "<<w<<‘\n’;
print_val(w);
cout <<"w after the function call is "<<w<<‘\n’; }
void print_val(int q)
{ cout<<"Value passed to the function is "<<q<<endl;
q = q *2; // doubles the value
cout<<"Value at the end of the function is "<< q <<endl;

39. Passing Data - by Value Output Value passed to the function is 3
w before the function call 3
Value passed to the function is 3
Value at the end of the function is 6
w after the function call is 3

40. Passing Data - by Reference
Syntax
double Pythagorus(double &, double &);
Pythagorus(height, base);
double Pythagorus(double& a, double& b)
function prototype
function call
function definition

41. Passing Data - by Reference
void main(void)
{ double height = 4.0, base = 3.0;
double Pythagorus(double &, double &);
cout << “Hypotenuse = “ << Pythagorus(height, base) << endl;
. . . }
double Pythagorus(double& a, double& b)
{ double c; c = sqrt(a*a + b*b);
return c;
address of height
address of base
* *

42. Passing Data - by Reference
address of height
address of base
double Pythagorus(double& a, double& b)
{ double c;
a++;
b++;
c = sqrt(a*a + b*b);
return c; }
back in main: cout << height;
cout << base: *

43. Passing Data - by Reference
In main() values referenced as
1 value stored a
height
1 value stored b
base
In Pythagorus() values referenced as *

44. Passing Data - by Reference{
float a, b, c, sum, product;
void calc(float, float, float, float &, float &); // prototype
cout << "Enter three numbers: ";
cin >> a >> b >> c;
calc(a, b, c, sum, product); // call
cout << a<<“ + “<<b<<“ + “c<<“ = " << sum;
cout << ‘\n’<<a<<“ * “<<b<<“ * “c<<“ = " << product; }
void calc(float x, float y, float z, float &tot, float& multiply)
{ tot = x + y + z; // definition
multiply = x * y * z;
x++; y++; z--; // for demo purposes

45. Passing Data - by Reference
Output Enter three numbers: = * 7 * 9 = 315
x is 6, y is 8, z is 8 tot and sum refer to the same address product and multiply refer to the same address *

46. Passing Data - by Reference
void main(void)
{ int w = 3;
void print_val(int &); // function prototype
cout <<"w before the function call is "<<w<<‘\n’;
print_val(w);
cout <<"w after the function call is "<<w<<‘\n’; }
void print_val(int& q)
{ cout<<"Value passed to the function is "<<q<<endl;
q = q *2; // doubles the value
cout<<"Value at the end of the function is "<< q <<endl;

47. Passing Data - by Reference
Output
w before the function call 3
Value passed to the function is 3
Value at the end of the function is 6
w after the function call is 6

48. Swap Routine void swap(float& num1, float& num2) { float temp;
temp = num1;
num1 = num2;
num2 = temp; }

49. Data Type Mismatch
value parameters implicit type conversion - value of the actual parameter is coerced to the data type of the formal parameter
reference parameters no coercion because an address is passed, not a value
* *

50. A Comparison formal actual parameter is parameter may be
value variable, constant, or expression type coercion may take place
reference variable only
of exact same type as formal

51. What’s Happening???? call sequence
1. memory is allocated 2. parameters are passed 3. transfer of control
return sequence
1. value of the return is stored memory is deallocated 3. transfer of control
* *

52. “Louis Pasteur’s theory of germs is ridiculous fiction.” Pierre Pachet
End Note
“Louis Pasteur’s theory of germs is ridiculous fiction.” Pierre Pachet
Professor of Physiology
Toulouse, 1872
Copyright © by Freedom TLC, Inc.

53. Function Practice - I: wholepart( )
accepts a double
returns the integer part of any fraction Hint: Assign the passed argument to an integer variable. Ex returns 123
the calling function displays the result
Bronson p

54. Function Practice - I: fracpart( )
accepts a double
returns the fractional part of any number passed to it. Ex returns .4567
the calling function displays the result
Bronson p

55. Function Practice - I: find_abs( )
accepts a double
computes its absolute value
returns the value
calling function displays the result
Bronson p

56. Function Practice - I: mult( )
accepts two doubles
multiplies them
returns the result
calling function displays the result
Bronson p

57. Function Practice - I: powfun( )
accepts two integers
raises the first to the power of the second
the returned value is a long integer
the calling function displays the result
Bronson p

58. Function Practice - I: tempvert( )
accepts a double
converts C to F or F to C
returns the converted temperature
the calling function asks the direction of conversion the temperature to convert displays the result
Bronson p
IN IN
double tempvert(double in_temp, char type) {
if (type == 'c' || type == 'C')
return( (5.0/9.0) * (in_temp ) );
else //if (type == 'f' || type == 'F')
return ((9.0/5.0) * in_temp ); }