C++学习————函数重载

输出字符串的前n个字符或者一个整数的前n位数

unsigned long left(unsigned long num, unsigned ct);//输出前n位数字
char * left(const char *str, int n = 1);//输出字符串的前n个字符

int main()
{
	char * trip = "Hawaii!!";
	unsigned long n = 12345678;
	int i;
	char * temp;

	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;
}