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2010-05-25T14:21:17Z

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==Demonstrate recursion==

<source lang="cpp">#include <iostream>
using namespace std;

int f(int n);

int main()
{
// use recursive version
cout << "4 factorial is " << f(4);

return 0;
}

int f(int n)
{
int answer;

if(n==1)
return(1);

answer = f(n-1)*n;
return(answer);
}</source>
<pre class=codeResult>4 factorial is 24</pre>

==Print a string backwards using recursion==

<source lang="cpp">#include <iostream>
using namespace std;

void f(char *s);

int main()
{
char str[] = "this is a test";

f(str);

return 0;
}

void f(char *s)
{
if(*s)
f(s+1);
else
return;

cout << *s;
}</source>
<pre class=codeResult>tset a si siht</pre>

==Recursive factorial function==

<source lang="cpp">#include <iostream>
using std::cout;
using std::endl;
#include <iomanip>
using std::setw;
unsigned long factorial( unsigned long ); // function prototype
int main()
{
for ( int counter = 0; counter <= 50; counter++ )
cout << setw( 2 ) << counter << "! = " << factorial( counter ) << endl;
return 0;
}
unsigned long factorial( unsigned long number )
{
if ( number <= 1 )
return 1;
else
return number * factorial( number - 1 );
}</source>
<pre class=codeResult>0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800
11! = 39916800
12! = 479001600
13! = 1932053504
14! = 1278945280
15! = 2004310016
16! = 2004189184
17! = 4006445056
18! = 3396534272
19! = 109641728
20! = 2192834560
21! = 3099852800
22! = 3772252160
23! = 862453760
24! = 3519021056
25! = 2076180480
26! = 2441084928
27! = 1484783616
28! = 2919235584
29! = 3053453312
30! = 1409286144
31! = 738197504
32! = 2147483648
33! = 2147483648
34! = 0
35! = 0
36! = 0
37! = 0
38! = 0
39! = 0
40! = 0
41! = 0
42! = 0
43! = 0
44! = 0
45! = 0
46! = 0
47! = 0
48! = 0
49! = 0
50! = 0</pre>

==The iterative factorial method.==

<source lang="cpp">#include <iostream>
using std::cout;
using std::endl;
#include <iomanip>
using std::setw;
unsigned long factorial( unsigned long );
int main()
{
for ( int counter = 0; counter <= 20; counter++ )
cout << setw( 2 ) << counter << "! = " << factorial( counter ) << endl;
return 0;
}
unsigned long factorial( unsigned long number )
{
unsigned long result = 1;
for ( unsigned long i = number; i >= 1; i-- )
result *= i;
return result;
}</source>
<pre class=codeResult>0! = 1
1! = 1
2! = 2
3! = 6
4! = 24
5! = 120
6! = 720
7! = 5040
8! = 40320
9! = 362880
10! = 3628800
11! = 39916800
12! = 479001600
13! = 1932053504
14! = 1278945280
15! = 2004310016
16! = 2004189184
17! = 4006445056
18! = 3396534272
19! = 109641728
20! = 2192834560</pre>

==The recursive fibonacci function.==

<source lang="cpp">#include <iostream>
using std::cout;
using std::cin;
using std::endl;
unsigned long fibonacci( unsigned long );
int main()
{
cout << "fibonacci( 20 ) = " << fibonacci( 20 ) << endl;
cout << "fibonacci( 30 ) = " << fibonacci( 30 ) << endl;
cout << "fibonacci( 35 ) = " << fibonacci( 35 ) << endl;
return 0;
}
unsigned long fibonacci( unsigned long number )
{
if ( ( number == 0 ) || ( number == 1 ) )
return number;
else
return fibonacci( number - 1 ) + fibonacci( number - 2 );
}</source>
<pre class=codeResult>fibonacci( 20 ) = 6765
fibonacci( 30 ) = 832040
fibonacci( 35 ) = 9227465</pre>

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