C++十六进制转十进制

#include"iostream"
#include"string"
#include"cmath"
using namespace std;
int main()
{
	string strHex;
       cin>>strHex;
	   string strBin="";
	   for(int j = 0 ; j < strHex.length() ; j++){
	   	switch(strHex[j]){
	   		case '0':strBin+="0000";break;
	   		case '1':strBin+="0001";break;
	   		case '2':strBin+="0010";break;
	   		case '3':strBin+="0011";break;
	   		case '4':strBin+="0100";break;
	   		case '5':strBin+="0101";break;
	   		case '6':strBin+="0110";break;
	   		case '7':strBin+="0111";break;
	   		case '8':strBin+="1000";break;
	   		case '9':strBin+="1001";break;
	   		case 'A':strBin+="1010";break;
	   		case 'B':strBin+="1011";break;
	   		case 'C':strBin+="1100";break;
	   		case 'D':strBin+="1101";break;
	   		case 'E':strBin+="1110";break;
	   		case 'F':strBin+="1111";break;
	   		default:break;
		   }
	   }
	  int len = strBin.length();
	  long long int sum=0;
	  for(int i = 0 ; i<strBin.length() ; i++){
	  	sum+=pow(2,len-1)*(strBin[i]-'0');
	  	len--;
	  }
	   cout<<sum;
   
	return 0;
}