函数：使用函数重载及默认参数实现程序

#include <iostream>

unsigned long left(unsigned long num, unsigned ct);
char * left(const char *str, int n=1);

int main(void)
{
	using namespace std;
	char *temp,*trip = "Hawaii!!";
	unsigned long n=12345678;
	int i;
	
	for(i=1; i<10; i++)
	{
		cout << left(n, i) << endl;
		temp = left(trip, i);
		cout << temp << endl;
		delete[] temp;
	}
	return 0;
}
unsigned long left(unsigned long num, unsigned ct)
{
	unsigned digits = 1;
	unsigned long n = num;
	
	if(ct == 0|| num == 0)return 0;
	
	while(n/=10) digits++;
	
	if(digits > ct)
	{
		ct=digits-ct;
		while(ct--) num/=10;
		
		return num;
	}
	else
		return num;
}
char * left(const char * str, int n)
{
	if(n < 0)
		n=0;
	char *p = new char[n+1];
	int i;
	for(i=0; i<n&&str[i]; i++) p[i]=str[i];
	
	while(i<=n) p[i++]='';
	
	
	return p;
}