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Ch8函数探幽/函数重载/leftover.cpp

+//leftover.cpp -- overloading the left()function
+#include <iostream>
+unsigned long left(unsigned long num, unsigned ct);
+char* left(const char* str, int n = 1);
+
+
+int main(void)
+{
+	using namespace std;
+	const char* trip = "Hawaii!!";		//test value
+	unsigned long n = 12345678;			//test value
+	int i;
+	char* temp;
+
+
+	for ( i = 0; i < 10; i++)
+	{
+		cout << left(n, i) << endl;
+		temp = left(trip, i);
+		cout << temp << endl;
+		delete[]temp;		//point to temporary storage
+	}
+	return 0;
+}
+
+
+//This function returns the first ct digits of the number num 
+unsigned long left(unsigned long num, unsigned ct)
+{
+	unsigned digits = 1;
+	unsigned long n = num;
+
+
+	if (ct == 0 || num == 0)
+	{
+		return 0;			//return 0 if no digits
+	}
+	while (n/=10)
+	{
+		digits++;
+	}
+	if (digits > ct)
+	{
+		ct = digits - ct;
+		while (ct--)
+		{
+			num /= 10;
+		}
+		return num;				//return left ct digits
+	}
+	else                      //if ct >= number of digits
+	{
+		return num;			  //return the whole number
+	}
+}
+
+
+
+//This function returns a pointer to a new string
+//consisting of the first n characters in the str string.
+
+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];			//copy characters
+
+	}
+	while (i <= n)
+	{
+		p[i++] = '\0';			//set rest of string to '\0'
+	}
+	return p;
+}