第四十三课 递归的思想与应用（上）

 

#include <iostream>
#include <cstring>
#include "DTString.h"

using namespace std;
using namespace DTLib;

unsigned int sum(unsigned int n)
{
    if( n > 1 )
    {
        return n + sum(n - 1);
    }
    else
    {
        return 1;
    }
}

int main()
{
    cout << sum(100) << endl;

    return 0;
}

#include <iostream>
#include <cstring>
#include "DTString.h"

using namespace std;
using namespace DTLib;

unsigned int sum(unsigned int n)
{
    if( n > 1 )
    {
        return n + sum(n - 1);
    }
    else
    {
        return 1;
    }
}

unsigned int fac(unsigned int n)
{
    if( n > 2 )
    {
        return fac(n - 1) + fac(n - 2);
    }

    if( (n == 2) || (n == 1) )
    {
        return 1;
    }

    return 0;
}

int main()
{
    cout << sum(100) << endl;

    for(int i = 1; i <= 10; i++)
    {
        cout << i << " : " << fac(i) << endl;
    }

    return 0;
}

#include <iostream>
#include <cstring>
#include "DTString.h"

using namespace std;
using namespace DTLib;

unsigned int sum(unsigned int n)
{
    if( n > 1 )
    {
        return n + sum(n - 1);
    }
    else
    {
        return 1;
    }
}

unsigned int fac(unsigned int n)
{
    if( n > 2 )
    {
        return fac(n - 1) + fac(n - 2);
    }

    if( (n == 2) || (n == 1) )
    {
        return 1;
    }

    return 0;
}

unsigned int _strlen_(const char* s)
{
    if( *s != '' )
    {
        return 1 + _strlen_(s+1);
    }
    else
    {
        return 0;
    }
}

int main()
{
    cout << _strlen_("Hello World") << endl;

    return 0;
}

 代码改进：

unsigned int _strlen_(const char* s)
{
    return s ? (*s ? (1 + _strlen_(s + 1)) : 0) : 0;
}

小结：