C++ 代码问题分析：进制转换程序的错误及修正

#include \u0026lt;string>\nusing namespace std;\n\nunsigned long long convertToDecimal(string s, unsigned long long x) {\n unsigned long long h = 0, w = 1;\n for(int i = s.size() - 1; i >= 0; i--) {\n h += (s[i] <= '9') ? ((s[i] - 48) * w) : ((s[i] - 87) * w);\n w = w * x;\n }\n return h;\n}\n\nstring convertFromDecimal(string c, unsigned long long a, unsigned long long b) {\n unsigned long long n = convertToDecimal(c, a);\n string y = '';\n if(b == 10) {\n return to_string(n); \n }\n while(n > 0) {\n int g = n % b;\n if(g < 10) {\n y = char(g + 48) + y;\n } else {\n y = char(g % b + 87) + y;\n }\n n = n / b;\n }\n return '(' + y + ') + to_string(b);\n}\n\nint main() {\n string c;\n cin >> c;\n unsigned long long a, b;\n cin >> a >> b;\n cout << convertFromDecimal(c, a, b) << endl;\n return 0;\n}