Transcript function example_2014_1

GE 211
Function in C++
Dr. Ahmed Telba
3.3 Math Library Functions
• Defining a Function:
• The general form of a C++ function definition
is as follows:
• return_type function_name( parameter list ) {
body of the function }Example
cout << sqrt( 900.0 );
– sqrt (square root) function The preceding
statement would print 30
– All functions in math library return a double
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A C++ function definition consists of a function header and a function body. Here are all the parts of a
function:
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Return Type: A function may return a value. The return _type is the data type of the value the function
returns. Some functions perform the desired operations without returning a value. In this case, the
return_type is the keyword void.
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Function Name: This is the actual name of the function. The function name and the parameter list
together constitute the function signature.
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Parameters: A parameter is like a placeholder. When a function is invoked, you pass a value to the
parameter. This value is referred to as actual parameter or argument. The parameter list refers to the
type, order, and number of the parameters of a function. Parameters are optional; that is, a function
may contain no parameters.
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Function Body: The function body contains a collection of statements that define what the function
does.
Functions That Use Parameters
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#include <iostream>
using namespace std;
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int main ()
{
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printAhmed(999);
return 0;
}
void printAhmed(int a)
{
cout<<"Ahmed "<<a<<endl;
Functions That Use Multiple Parameters
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#include<iostream>
using namespace std;
int addnum (int x,int y)
{
int answer=x+y;
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return answer;
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}
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int main()
{
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cout<<"The Result is integer = "<<addnum (33,55)<< endl ;
return 0;
}
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// function returning the max between two numbers
#include <iostream>
using namespace std;
// function declaration
int max(int num1, int num2);
int main ()
{ // local variable declaration:
int a = 100; int b = 200; int ret;
// calling a function to get max value.
ret = max(a, b);
cout << "Max value is : " << ret << endl;
return 0; }
// function returning the max between two numbers
int max(int num1, int num2)
{
// local variable declaration
int result;
if (num1 > num2)
result = num1;
else
result = num2;
return result; }
Function Arguments:
Call Type
Description
Call by value
This method copies the actual value of an argument
into the formal parameter of the function. In this
case, changes made to the parameter inside the
function have no effect on the argument.
Call by pointer
This method copies the address of an argument into
the formal parameter. Inside the function, the
address is used to access the actual argument used
in the call. This means that changes made to the
parameter affect the argument.
Call by reference
This method copies the reference of an argument
into the formal parameter. Inside the function, the
reference is used to access the actual argument used
in the call. This means that changes made to the
parameter affect the argument.
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#include <iostream>
using namespace std;
int mult ( int x, int y );
int main()
{
int x;
int y;
cout<<"Please input two numbers to be multiplied: ";
cin>> x >> y;
cin.ignore();
cout<<"The product of your two numbers is "<< mult ( x, y ) <<"\n";
cin.get();
}
int mult ( int x, int y )
{
return x * y;
//return (9);
}
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#include <iostream>
using namespace std;
int sum(int a, int b=20)
{
int result;
result = a + b;
return (result);
}
int main ()
{
// local variable declaration:
int a = 100;
int b = 200;
int result;
// calling a function to add the values.
result = sum(a, b);
cout << "Total value is :" << result << endl;
// calling a function again as follows.
result = sum(a);
cout << "Total value is :" << result << endl;
return 0;
}
3.3 Math Library Functions
• Function arguments can be
– Constants
• sqrt( 4 );
– Variables
• sqrt( x );
– Expressions
• sqrt( sqrt( x ) ) ;
• sqrt( 3 - 6x );
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M e tho d
ceil( x )
De sc rip tio n
Exa m p le
rounds x to the smallest integer ceil( 9.2 ) is 10.0
not less than x
ceil( -9.8 ) is -9.0
cos( x )
trigonometric cosine of x
cos( 0.0 ) is 1.0
(x in radians)
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
floor( 9.2 ) is 9.0
not greater than x
floor( -9.8 ) is -10.0
fmod( x, y )
remainder of x/y as a floating- fmod( 13.657, 2.333 ) is 1.992
point number
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
sin( 0.0 ) is 0
(x in radians)
sqrt( x )
square root of x
sqrt( 900.0 ) is 30.0
sqrt( 9.0 ) is 3.0
tan( x )
trigonometric tangent of x
tan( 0.0 ) is 0
(x in radians)
Fig . 3.2 M a th lib ra ry func tio ns.
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3.4 Functions
• Functions
– Modularize a program
– Software reusability
• Call function multiple times
• Local variables
– Known only in the function in which they are defined
– All variables declared in function definitions are local variables
• Parameters
– Local variables passed to function when called
– Provide outside information
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3.5 Function Definitions
• Function prototype
– Tells compiler argument type and return type of
function
– int square( int );
• Function takes an int and returns an int
– Explained in more detail later
• Calling/invoking a function
– square(x);
– Parentheses an operator used to call function
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• Pass argument x
• Function gets its own copy of arguments
3.5 Function Definitions
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Format for function definition
return-value-type function-name( parameter-list )
{
declarations and statements
}
– Parameter list
• Comma separated list of arguments
– Data type needed for each argument
• If no arguments, use void or leave blank
– Return-value-type
• Data type of result returned (use void if nothing returned)
3.5 Function Definitions
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Example function
int square( int y )
{
return y * y;
}
return keyword
– Returns data, and control goes to function’s caller
• If no data to return, use return;
– Function ends when reaches right brace
• Control goes to caller
Functions cannot be defined inside other functions
Next: program examples
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#include<iostream> // random number generator
#include<cstdlib>
using namespace std;
int main()
{
for (int x=1;x<25;x++)
{
cout<<"The Random number is = "<<rand()<< endl ;
} }
------#include<iostream>
#include<cstdlib>
using namespace std;
int main()
{
for (int x=1;x<25;x++)
{
cout<<"The Random number is = "<<rand()%6 << endl ; //generate 0 to 5
}
}
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#include<iostream>
using namespace std;
// print string word
void print();
main()
{
print();
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}
void print()
{
cout<<"I am c++";
}
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#include <iostream>
using namespace std;
// add number from 1:50
int sum(int);
int main ()
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{
int x ;
cout<<" sumion is :- "<<sum (x) ;
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}
int sum (int a)
{
int su =0 ;
for(int i=1 ; i<=50 ;i++)
su+=i ;
return su ;
}
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#include<iostream>
using namespace std;
//vectorial of used number
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int mult(int);
main()
{
int n;
cin>>n;
cout<<mult(n);
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}
int mult(int x)
{int i,mult=1;
for(i=1;i<=x;i++)
mult=mult*i;
return mult ;
}
// function overloading
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#include<iostream>
using namespace std;
void print(int x)
{
cout<<"The Result is integer = "<<x<< endl ;
}
void print(double x)
{
cout<<"The Result is double = "<<x<< endl ;
}
void print(char x)
{
cout<<"The Result is char = "<<x<< endl ;
}
int main( )
{
print(33.114);
print('k');
print(44);
return 0;
}
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#include<iostream>
using namespace std;
float max(int x , float y)
{
if(x > y)
return x;
return y;
}
main() {
cout<<max(5,5.4);
}
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#include<iostream>
using namespace std;
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int sum()
{
int x = 5 , y = 4;
return x + y;
}
main()
{
int z = sum();
cout<<z;
return 0;
}
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#include <iostream> // solve equation x^2+25
using namespace std;
int tow(int) ;
int main()
{
int x ;
cout<<"Enter the number x : "<<endl ;
cin>>x ;
cout<<"y=x*x +25 = "<<tow(x) <<endl ;
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}
int tow(int p)
{
int y ;
y= (p*p)+25 ;
return y ;
}
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#include <iostream>// cubic of x=x^3
#include <cmath>
using namespace std;
int sqrt (int) ;
int main ()
{
int x ;
cout<<"Enter x " ;
cin>>x ;
cout<<"The sqrt of "<<x <<" = "<<sqrt(x) ;
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}
//end main
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int sqrt (int a)
{
return (a*a*a) ;
}
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#include <iostream>
#include <cmath>
using namespace std;
void maths( ) ;
int main ()
{
maths();
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}
void maths( )
{
int sum =0 ;
int x , n ;
cout<<"Enter base number : " ;
cin>>x ;
cout<<"Enter power number : " ;
cin>>n ;
for (int i=2 ; i<=n ; i+=2) {
sum=pow(x,i) ;
sum+=sum;
}
cout<<"The Resulit = "<<sum ;
}
// solving equation of x=x^n
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#include<iostream> //Odd & Even number
using namespace std;
main(){
for(int i=1;i<=100;i++)
if(i%2==0)
cout<<i<<" : Even ."<<"\n";
else
if(i%2==1)
cout<<i<<" : Odd ."<<" \t";}
Random Number Generator
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#include <iostream>
#include <cstdlib>
using namespace std;
int main( )
{
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int i;
srand(99);
for (i = 0; i < 10; i++)
cout << (rand( ) % 11) << endl ;
srand(99);
for (i = 0; i < 10; i++)
cout << (rand( ) % 11) << endl ;
return 0;
}
// compound assignment operators
#include <iostream>
using namespace std;
int main ()
{
int a, b=3;
a = b;
a+=2;
cout << a;
return 0;
}
a =5
// equivalent to a=a+2
Increase and decrease (++, --)
• Increase and decrease (++, --)
• Shortening even more some expressions, the
increase operator (++) and the decrease
operator (--) increase or reduce by one the
value stored in a variable. They are equivalent
to +=1 and to .=1, respectively. Thus:
• c++; === c+=1; === c=c+1;
Bitwise Operators ( &, |, ^, ~, <<, >> )
Bitwise operators modify variables considering the bit patterns that represent the values they store.
a = 5 + (7 % 2) // with a result of 6, or
a = (5 + 7) % 2 // with a result of 0
Standard Output (cout)
• By default, the standard output of a program
is the screen, and the C++ stream object
defined to access it is cout.
• cout is used in conjunction with the insertion
operator, which is written as << (two "less
than" signs).
Input output
• // i/o example
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#include <iostream>
using namespace std;
int main ()
{
int i;
cout << "Please enter an integer value: ";
cin >> i;
cout << "The value you entered is " << i;
cout << " and its double is " << i*2 << ".\n";
return 0;
}
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You can also use cin to request more than one datum input from the user:
cin >> a >> b;
is equivalent to:
cin >> a;
cin >> b;
cin and strings
We can use cin to get strings with the extraction operator (>>) as we do with
fundamental data type variables:
cin >> mystring;
// cin with strings
#include <iostream>
#include <string>
using namespace std;
int main ()
{
string mystr;
cout << "What's your name? ";
getline (cin, mystr);
cout << "Hello " << mystr << ".\n";
cout << "What is your favorite team? ";
getline (cin, mystr);
cout << "I like " << mystr << " too!\n";
return 0;
}
// stringstreams
#include <iostream>
#include <string>
#include <sstream>
using namespace std;
int main ()
{
string mystr;
float price=0;
int quantity=0;
cout << "Enter price: ";
getline (cin,mystr);
stringstream(mystr) >> price;
cout << "Enter quantity: ";
getline (cin,mystr);
stringstream(mystr) >> quantity;
cout << "Total price: " << price*quantity <<
endl;
return 0;
}
if (x == 100)
cout << "x is 100";
else
cout << "x is not 100";
--if (x > 0)
cout << "x is positive";
else if (x < 0)
cout << "x is negative";
else
cout << "x is 0";
The while loop
// custom countdown using while
#include <iostream>
using namespace std;
int main ()
{
int n;
cout << "Enter the starting number > ";
cin >> n;
while (n>0) {
cout << n << ", ";
..n;
}
cout << "FIRE!\n";
return 0;
}
// countdown using a for loop
#include <iostream>
using namespace std;
int main ()
{
for (int n=10; n>0; n..) {
cout << n << ", ";
}
cout << "FIRE!\n";
return 0;
}
switch (x) {
case 1:
case 2:
case 3:
cout << "x is 1, 2 or 3";
break;
default:
cout << "x is not 1, 2 nor 3";
}
Functions (I)
Using functions we can structure our programs in a more modular way, accessing all the potential
that structured
programming can offer to us in C++.
A function is a group of statements that is executed when it is called from some point of the
program. The
following is its format:
type name ( parameter1, parameter2, ...) { statements }
where:
• type is the data type specifier of the data returned by the function.
• name is the identifier by which it will be possible to call the function.
• parameters (as many as needed): Each parameter consists of a data type specifier followed by
an
identifier, like any regular variable declaration (for example: int x) and which acts within the
function as
a regular local variable. They allow to pass arguments to the function when it is called. The
different
parameters are separated by commas.
• statements is the function's body. It is a block of statements surrounded by braces { }.
// function example
#include <iostream>
using namespace std;
int subtraction (int a, int b)
{
int r;
r=a - b;
return (r);
}
int main ()
{
int x=5, y=3, z;
z = subtraction (7,2);
cout << "The first result is " << z << '\n';
cout << "The second result is " << subtraction (7,2) << '\n';
cout << "The third result is " << subtraction (x,y) << '\n';
z= 4 + subtraction (x,y);
cout << "The fourth result is " << z << '\n';
return 0;
}
// void function example
#include <iostream>
using namespace std;
void printmessage ()
{
cout << "I'm a function!";
}
int main ()
{
printmessage ();
return 0;
}
// passing parameters by reference
#include <iostream>
using namespace std;
void duplicate (int& a, int& b, int& c)
{
a*=2;
b*=2;
c*=2;
}
int main ()
{
int x=1, y=3, z=7;
duplicate (x, y, z);
cout << "x=" << x << ", y=" << y << ", z=" << z;
return 0;
}
// more than one returning value
#include <iostream>
using namespace std;
void prevnext (int x, int& prev, int& next)
{
prev = x-1;
next = x+1;
}
int main ()
{
int x=100, y, z;
prevnext (x, y, z);
cout << "Previous=" << y << ", Next=" << z;
return 0;
}
// default values in functions
#include <iostream>
using namespace std;
int divide (int a, int b=2)
{
int r;
r=a/b;
return (r);
}
int main ()
{
cout << divide (12);
cout << endl;
cout << divide (20,4);
return 0;
}
// /*we have only specified one argument, but the function divide allows up to two. So the function
divide has
assumed that the second parameter is 2 since that is what we have specified to happen if this
parameter was not
passed (notice the function declaration, which finishes with int b=2, not just int b). Therefore the result
of this
function call is 6 (12/2). */
• Overloaded functions.
• In C++ two different functions can have the
same name if their parameter types or
number are different. That
• means that you can give the same name to
more than one function if they have either a
different number of
• parameters or different types in their
parameters. For example:
// overloaded function
#include <iostream>
using namespace std;
int operate (int a, int b)
{
return (a*b);
}
float operate (float a, float b)
{
return (a/b);
}
int main ()
{
int x=5,y=2;
float n=5.0,m=2.0;
cout << operate (x,y);
cout << "\n";
cout << operate (n,m);
cout << "\n";
return 0;
}
Function
// factorial calculator
#include <iostream>
using namespace std;
long factorial (long a)
{
if (a > 1)
return (a * factorial (a-1));
else
return (1);
}
int main ()
{
long number;
cout << "Please type a number: ";
cin >> number;
cout << number << "! = " << factorial (number);
return 0;
}
// declaring functions prototypes
#include <iostream>
using namespace std;
void odd (int a);
void even (int a);
int main ()
{
int i;
do {
cout << "Type a number (0 to exit): ";
cin >> i;
odd (i);
} while (i!=0);
return 0;
}
void odd (int a)
{
if ((a%2)!=0) cout << "Number is odd.\n";
else even (a);
}
void even (int a)
{
if ((a%2)==0) cout << "Number is even.\n";
else odd (a);
}
#include <iostream.h>
main ( )
{
cout << 7 << " is an integer.\n";
cout << 'a' << "is a character.\n";
}
#include<iostream>
using namespace std;
main ( )
{
cout<<10;
cout<<20<<30;
return 0;
}
• cout<<10<< '\n';
• cout<<20<<30<< '\n';
#include <iostream>
//#include <conio>
using namespace std;
// Program 1-4: Addition program
//#include<iostream.h>
#include<conio.h>
main ( ) {
int integer1, integer2, sum;
cout <<"Enter first integer\n";
cin >> integer1;
cout <<"Enter second integer\n";
cin >> integer2;
sum= integer1+integer2;
cout <<"sum="<<sum<<endl;
getch();
return 0;
}
• cin >> integer1>>integer2
• cout<<''sum= ''<<sum<<endl
• C=(f-32)*5/9;
#include <iostream.h>
main ( )
{
int grade ;
cout << " Enter the grade";
cin >>grade;
if(grade>= 50)
cout<<"pass" <<endl;
else
cout <<"fail"<<endl;
return 0;
}
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if (gender==1)
cout<<women <<endl;
else
cout <<man<<endl;
Formats in cpp:
#include<iostream.h>
main ( )
{
int n;
cin >> n;
cout<< “ n after adding 2 = “ << a+= 2 <<endl;
cout<< “ n after a subtracting 2 = “ << a-= 2 <<endl;
cout<< “ n after dividing by 2 = “ << a/= 2 <<endl;
cout<< “ n after multiplying by 2 = “ << a*= 2 <<endl;
cout<< “ n mod 2 = “ << a %= 2 <<endl;
return 0;
}
#include<iostream.h>
main ( )
{
int c;
c = 5;
cout << c << endl;
cout << c++ <<endl;
cout << c <<endl;
c=5;
cout << c << endl << endl;
cout << ++c << endl;
cout << c << endl;
system("pause");
return 0;
}
Logic operations
#include<iostream.h>
main ( )
{
int counter, grade, total ,average;
total = 0;
counter = 1;
//while (counter <= 10)
while (counter <= 0) {
cout<< “ Enter grade : “;
cin >>grade;
total = total + grade;
counter = counter + 1;
}
cout<<endl;
average = total /10;
//Continued
cout << “ Class average is: “ << average <<endl;
return 0;
• Counter
#include<iostream>
using namespace std;
int main ( )
{
for (int j=10; j<=100; j+=10)
cout <<j<<endl;
system("pause");
return 0;
}
Function in c++
#include<iostream.h>
int square(int);//function prototype
main()
{
for(int x=1;x<=10;x++)
cout<<square(x)<<" ";
cout<<endl;
}
//now function definition
int square(int y)
{
return y*y;
}
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#include <iostream>
using namespace std;
int main ()
{
// local variable declaration:
int a = 100;
// check the boolean condition
if( a < 20 )
{
// if condition is true then print the following
cout << "a is less than 20;" << endl;
}
else
{
// if condition is false then print the following
cout << "a is not less than 20;" << endl;
}
cout << "value of a is : " << a << endl;
return 0;
}
// function example
#include <iostream>
using namespace std;
int addition (int a, int b)
{
int r;
r=a+b;
return (r);
}
int main ()
{
int z;
z = addition (5,3);
cout << "The result is " << z <<endl; ;
return 0;
}
Function in C++
function example
#include <iostream>
using namespace std;
int subtraction (int a, int b)
{
int r;
r=a-b;
return (r);
}
int main ()
{
int x=5, y=3, z;
z = subtraction (7,2);
cout << "The first result is " << z << '\n';
cout << "The second result is " << subtraction (7,2) << '\n';
cout << "The third result is " << subtraction (x,y) << '\n';
z= 4 + subtraction (x,y);
cout << "The fourth result is " << z << '\n';
return 0;
}
void function example
#include <iostream>
using namespace std;
void printmessage ()
{
cout << "I'm a function!" << '\n‘;
}
int main ()
{
printmessage ();
return 0;
}
// passing parameters by reference
#include <iostream>
using namespace std;
void duplicate (int& a, int& b, int& c)
{
a*=2;
b*=2;
c*=2;
}
int main ()
{
int x=1, y=3, z=7;
duplicate (x, y, z);
cout << "x=" << x << ", y=" << y << ", z=" << z;
return 0;
}
// more than one returning value
#include <iostream>
using namespace std;
void prevnext (int x, int& prev, int& next)
{
prev = x-1;
next = x+1;
}
int main ()
{
int x=100, y, z;
prevnext (x, y, z);
cout << "Previous=" << y << ", Next=" << z;
return 0;
}
// default values in functions
#include <iostream>
using namespace std;
int divide (int a, int b=2)
{
int r;
r=a/b;
return (r);
}
int main ()
{
cout << divide (12);
cout << endl;
cout << divide (20,4);
return 0;
}
// overloaded function
#include <iostream>
using namespace std;
int operate (int a, int b)
{
return (a*b);
}
float operate (float a, float b)
{
return (a/b);
}
int main ()
{
int x=5,y=2;
float n=5.0,m=2.0;
cout << operate (x,y);
cout << "\n";
cout << operate (n,m);
cout << "\n";
return 0;
}
• Recursivity.
• Recursivity is the property that functions have to be
called by themselves. It is useful for many tasks, like
sorting or calculate the factorial of numbers. For
example, to obtain the factorial of a number (n!) the
mathematical formula would be:
n! = n * (n-1) * (n-2) * (n-3) ... * 1
more concretely, 5! (factorial of 5) would be:
5! = 5 * 4 * 3 * 2 * 1 = 120
and a recursive function to calculate this in C++ could
be:
// factorial calculator
#include <iostream>
using namespace std;
long factorial (long a)
{
if (a > 1)
return (a * factorial (a-1));
else
return (1);
}
int main ()
{
long number;
cout << "Please type a number: ";
cin >> number;
cout << number << "! = " << factorial (number);
return 0;
}
Declaring functions
•
Until now, we have defined all of the functions before the first appearance of calls to them in the
source code. These calls were generally in function main which we have always left at the end of
the source code. If you try to repeat some of the examples of functions described so far, but placing
the function main before any of the other functions that were called from within it, you will most
likely obtain compiling errors. The reason is that to be able to call a function it must have been
declared in some earlier point of the code, like we have done in all our examples.
But there is an alternative way to avoid writing the whole code of a function before it can be used
in main or in some other function. This can be achieved by declaring just a prototype of the
function before it is used, instead of the entire definition. This declaration is shorter than the entire
definition, but significant enough for the compiler to determine its return type and the types of its
parameters.
Its form is:
type name ( argument_type1, argument_type2, ...);
It is identical to a function definition, except that it does not include the body of the function itself
(i.e., the function statements that in normal definitions are enclosed in braces { }) and instead of
that we end the prototype declaration with a mandatory semicolon (;).
The parameter enumeration does not need to include the identifiers, but only the type specifiers.
The inclusion of a name for each parameter as in the function definition is optional in the prototype
declaration. For example, we can declare a function called protofunction with two int parameters
with any of the following declarations:
// declaring functions prototypes
#include <iostream>
using namespace std;
void odd (int a);
void even (int a);
int main ()
{
int i;
do {
cout << "Type a number (0 to exit): ";
cin >> i;
odd (i);
} while (i!=0);
return 0;
}
void odd (int a)
{
if ((a%2)!=0) cout << "Number is odd.\n";
else even (a);
}
void even (int a)
{
if ((a%2)==0) cout << "Number is even.\n";
else odd (a);
system("pause");
}