leftover.cpp

一本很好的C++学习的丛书！初学者必看的

// 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()
{
     using namespace std;
    char * trip = "Hawaii!!";   // test value
    unsigned long n = 12345678; // test value
    int i;
    char * temp;

    for (i = 1; 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; 
}