《C++程序设计语言》6.6_16 包含数字的C风格字符串为参数, 返回与之对应的int值

/*-----------------------------------------------------写一个函数atoi(const char*),它以一个包含数字的C风格字符串为参数,返回与之对应的int值. 例如, atoi("123")应是123. 修改atoi(), 使之除了能处理简单的十进制数之外, 还能处理C++的八进制和十六进制记法形式.修改atoi()以处理C++的字符常量记法.-----------------------------------------------------*/#include <iostream>#include <string>#include <math.h>using std::cout;using std::cin;using std::endl;using std::string;const int N = 20;char* create(){cout << "Please input a string of numbers(0~9):\n";char* cch = new char[N];int i = 0;char ch;for (; i < N-1; i++){ch = cin.get();if (ch != '\n')cch[i] = ch;elsebreak;}cch[i] = '\0';return cch;}void show(char* sch){cout << "Output the string:\n";puts(sch);}int atoi(char* ach){cout << "Converts a string to an integer:\n";int anum = 0;int l = strlen(ach);for (int i = 0; i < l; i++)anum += (ach[i]-48) * pow(10, l-i-1);cout << "How do you want to output the number(oct、dec or hex):\n";string str;cin >> str;if (str == "oct")cout << std::oct;else if (str == "hex")cout << std::hex;elsecout << std::dec;return anum;}int  main(){int num;char *ch;ch = create();show(ch);num = atoi(ch);cout << num << endl;return 0;}