C++测验代码

 /*
     返回字符串前n位和返回整数前n位
 */

 #include <iostream>

 unsigned long left(unsigned long num, int n);
 char * left(char * str, int n);

 using namespace std;

 int main()
 {
     unsigned long  num;
     int n;
     cout << "请输入一个整数:";
     cin >> num;
     cout << "请输入要截取的位数:";
     cin >> n;
     cout << "前" << n << "位为" << left(num, n) << endl;

     char * str = new char();
     cout << "请输入一个字符串:";
     cin >> str;
     cout << "请输入要截取的位数:";
     cin >> n;
     cout << "前" << n << "位为" << left(str, n) << endl;

     //delete[] str;

     cin.get();
     cin.get();
 }

 unsigned long left(unsigned long num, int n)
 {
     unsigned long len = ;    //表示这个数一共有几位
     unsigned long temp_num = num;
     while (temp_num /= )
     {
         len++;
     }
     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
     while (cut_num_len--)
     {
         num /= ;
     }
     return num;
 }

 char * left(char * str, int n)
 {
     int len = strlen(str);
     n = n >= len ? len : n;
     char * temp_char = new char(n + );

     for (int i = ; i < n; i++) {
         *(temp_char + i) = *(str + i);
     }
     temp_char[n] = '\0';
     return temp_char;
 }

大家看下，有一个问题，当我取消//delete[] str;注释后，程序会报错，不是鼓励如果是用new自成的指针最好要delete掉的吗？求正确答案。