写出一个程序，接受一个十六进制的数，输出该数值的十进制表示。（多组同时输入 ）

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#include <iostream> #include <string> #include <cmath>   int main() {     std::string hex;     while(std::cin>>hex) {         int sum=0, flag=0;         for(std::string::const_reverse_iterator cit=hex.rbegin(); cit!=hex.rend()-2; ++cit) {             int digit;             if(*cit>='A' && *cit<='F') {                 digit = *cit - 'A' + 10;             }             else if(*cit>='a' && *cit<='f') {                 digit = *cit - 'a' + 10;             }             else {                 digit = *cit - '0';             }             sum += pow(16, flag) * digit;             flag++;         }         std::cout<<sum<<std::endl;     }     return 0; }