C++ Tutorial/Function/function recursion

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>

4 factorial is 24

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>

tset a si siht

Recursive factorial function

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. 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>

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

The iterative factorial method.

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. 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>

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

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>

fibonacci( 20 ) = 6765
fibonacci( 30 ) = 832040
fibonacci( 35 ) = 9227465