1 /* 2     返回字符串前n位和返回整数前n位 3 */ 4  5 #include <iostream> 6  7 unsigned long left(unsigned long num, int n); 8 char * left(char * str, int n); 9 10 using namespace std;11 12 int main()13 {14     unsigned long  num;15     int n;16     cout << "请输入一个整数:";17     cin >> num;18     cout << "请输入要截取的位数:";19     cin >> n;20     cout << "前" << n << "位为" << left(num, n) << endl;21 22     char * str = new char(20);23     cout << "请输入一个字符串:";24     cin >> str;25     cout << "请输入要截取的位数:";26     cin >> n;27     cout << "前" << n << "位为" << left(str, n) << endl;28 29     //delete[] str;30 31     cin.get();32     cin.get();33 }34 35 36 unsigned long left(unsigned long num, int n)37 {38     unsigned long len = 1;    //表示这个数一共有几位39     unsigned long temp_num = num;40     while (temp_num /= 10)41     {42         len++;43     }44     unsigned long cut_num_len = len - (unsigned long(n) >= len ? len : unsigned long(n));    //当n小于整数的长度时，直接取回原来的整数45     while (cut_num_len--)46     {47         num /= 10;48     }49     return num;50 }51 52 char * left(char * str, int n)53 {54     int len = strlen(str);55     n = n >= len ? len : n;56     char * temp_char = new char(n + 1);57 58     for (int i = 0; i < n; i++) {59         *(temp_char + i) = *(str + i);60     }61     temp_char[n] = ‘\0‘;62     return temp_char;63 }