Object Oriented ProgrammingSpring - 2012

COMSATS Institute of Information Technology

FunctionsOOP in C++ by Robert Lafore - Chapter#5

Kaleem Ullahkaleemullah@ciitvehari.edu.pk

2

Overloaded functions

int main()

{

repchar();

repchar(‘=’);

repchar(‘+’, 30);

return 0;

}

3

Overloaded functions

4

Overloaded functions: Different kinds of arguments

• struct Distance • {• int feet;• float inches;• };

Void disp( Distance ); //declarations

Void disp( float );

5

Overloaded functions: Different kinds of arguments

• struct Distance • {• int feet;• float inches;• };

Void disp( Distance ); //declarations

Void disp( float );

6

Properties of recursive functions

1. Base Case(s): condition for terminating the recursive process

2. Recursive Case(s): set of rules to break the problem into smaller sub-problems to reach base case

a) Divide the problem into smaller sub-problems

b) Solve the sub-problems

c) Combine results to get answer

Sub-problems solved as a recursive call to the same function

7

int loop(int x) {

return (1 + loop(x))}

infinite loop – no termination

• Trace Table with x=5

1 + loop 5

Problem not being divided into smaller problems – no termination

1 + loop 5

…

loop 5

Need of Base Case and Recursive Case

Recursive function with

– no base case

– not a valid recursive case

8

Power function• Lets figure out a recursive function for

calculating the Powers of a given number

2nd power functionSquare of x = x*x

3rd power functionCube of x = x*x*x

4th power functionFourth Power of x = x*x*x*x

9

Power function

x4 = x*x*x*x = x*( x*x*x ) = x*x3

x5 = x*x*x*x*x = x*(x*x*x*x ) = x*x4

x6 = x*x*x*x*x*x = x*(x*x*x*x*x ) = x*x5

In general

xn = x*xn-1

Int power (int x, int n)

{

return x * power (x, n-1)

}

10

Power Function

When does it stop ?

Int power (int x, int n)

{

return x * power (x, n-1)

}

Step no.Calc 23: Power (2,3)x=2, n=3

1 2* power(2,2)

2 2* 2* power(2,1)

3 2*2* 2*power(2,0)

4 2*2*2* 2*power(2,-1)

x * power (x, n-1)

We need to stop here

We know 20=1

Base case: if n==0 return 1

Trace table

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Revised Power FunctionInt power (int x, int n)

{

If (n==0)

return 1;

else

return x * power (x, n-1)

}

Result: 8

Base case

Recursive case

sub-problems must be “smaller” than the original problem otherwise the recursion never terminates.

Trace table: Calc 23: x=2, n=3

Power (2,3)

2* power(2,2)

2* 2* power(2,1)

2*2* 2*power(2,0)

1

2

4

=8

12

Factorial function

Factorial 0! = 1

1! = 1

2! = 2 * 1 = 2

3! = 3 * 2 * 1 = 6

4! = 4 * 3 * 2 * 1 = 24

13

Factorial function

0! = 1

1! = 1

2! = 2 * 1 = 2

3! = 3 * 2 * 1 = 6

4! = 4 * 3 * 2 * 1 = 244*3!

3*2!

2*1!

1*0!

……

In general: n!=n*(n-1)!

Recursive case: Factorial(n)=n*factorial(n-1)

Base case: 0!=1 i.e; if (n==0) return 1

14

Factorial functionInt factorial (int n){If (n==0)

return 1;else

return n * factorial (n-1)}

Trace table: Calc 4! here n=4

factorial (4)

4* factorial (3)

4* 3* factorial (2)

4*3* 2* factorial (1)

4*3*2* 1* factorial (0)11

26

=24

15

Factorial function

Version Action Argument or Return Value1 Call 52 Call 43 Call 34 Call 25 Call 15 Return 14 Return 23 Return 62 Return 241 Return 120

16

Fibonacci sequence

The first ten terms in the sequence are:

1,1,2,3,5,8,13,21,34,55

Each value, except for first two, is sum of last two values

Simply saying:Fib(n)= fib(n-1)+fib(n-2) except for when n=0 and n=1

Base case: if (n==0 or n==1)Return 1

Recursive case: Fib(n)= fib(n-1)+fib(n-2)

17

Function for fibonacci sequenceInt fib (int n){If (n==0 or n==1)

return 1;else

return fib(n-1) +fib (n-2);}

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Trace of Fibonacci(5)

fib 5

fib 4 + fib 3

fib 3 + fib 2 fib 2 + fib 1

fib 2 + fib 1 fib 1 + fib 0 fib 1 + fib 0

fib 1 + fib 0

= 8

If (n==0 or n==1)return 1;elsereturn fib(n-1) +fib (n-2);

3 2

5 3

2

2 1

11

1

1

111

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Why recursion?• Recursion makes the

program faster?• Recursion uses less

memory?

• Recursion makes the code much simpler and Easy to read

20

In-Line functions• Functions save memory space because

call to function cause the same code to be executed

• When a function is called, jump to function is made. After the call, jump back to instruction following the call

• takes some extra time for jump to function Slows down the program

• To save execution time for short functions having one or two statements) Make them inline

21

In-Line functions

22

In-Line functions: Example#include <iostream>

using namespace std;

inline float lbstokg(float pounds) // converts pounds to kilograms

{

return 0.453592 * pounds;

}

int main()

{

float lbs;

cout << “\nEnter your weight in pounds: “;

cin >> lbs;

cout << “Your weight in kilograms is “ << lbstokg(lbs)

<< endl;

return 0;

}

23

In-Line functions: Example• inline float lbstokg(float pounds) // inline function

• Sometimes the compiler will ignore the request and compile the function as a normal function.

• It might decide the function is too long to be inline, for instance.

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Default arguments• In OVERLOAD we used three different functions

with the same name to handle different numbers of arguments.

• Achieve the same effect in a different way!!

// demonstrates missing and default arguments

#include <iostream>

using namespace std;

void repchar(char=’*’, int=45); //declaration with default arguments

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Default arguments: Example• Achieve the same effect in a different way!!

int main()

{

repchar(); //prints 45 asterisks

repchar(‘=’); //prints 45 equal signs

repchar(‘+’, 30); //prints 30 plus signs

return 0;

}

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Default arguments: Example

void repchar(char ch, int n)

{

for(int j=0; j<n; j++) //loops n times

cout << ch; //prints ch

cout << endl;

}

27

Default arguments: Example

void repchar(char=’*’, int=45);

//declaration with default arguments

• The default argument follows an equal sign• Working in case of missing arguments?

One missing? Two missing? Remember that missing arguments must be those at the end of the

argument list!! Can’t miss first argument and provide second

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Static Variable• A static variable in kind of local variable (inside a function)

lifetime is the same as that of a global variable

• Does not exist until the first call to the function containing it is made

• remains in existence for the life of the program

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Static Variable: Examplevoid teststatic()

{

static int count; //automatically initialized to 0

count++;

cout<<"I am called "<<count<<" times"<<endl;

}

void main()

{

teststatic();

teststatic();

teststatic();

}

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Static Variable: Example

31

Non-Static Variable: Examplevoid teststatic()

{

int count=0; // initialized to 0, not a static variable

count++;

cout<<"I am called "<<count<<" times"<<endl;

}

int main()

{

teststatic();

teststatic();

teststatic();

}

32

Non-Static Variable: Example

33

Const function arguments• To assure that the function cannot change the value

passed

void testconst(int a, const int b )

{

a=10; //OK

b=10; //error

}

int main()

{

int x,y;

testconst(x,y);

}