16進制輸入到10進制輸出

常規算法： 

#include<iostream>
#include<string>
#include<cmath>
using namespace std;

int change(string a, int n)
{
	int sum = 0;
	int x, tmp, b;//x是當前位數0~n-1
	for (x = 0; n > 0; n--, x++)
	{
		//如果字符是數字
		if ((a[x] >= '0') && (a[x] <= '9'))
		{
			//b爲字符對應的10進制數值
			b = a[x] - '0';
			tmp = pow(16, n - 1);//當前位的16的次方
			tmp = tmp * b;//當前值
			sum = sum + tmp;

		}
		//如果字符是小寫字母
		else if ((a[x] >= 'a') && (a[x] <= 'f'))
		{
			b = a[x] - 'a' + 10;
			tmp = pow(16, n-1);
			tmp = tmp * b;
			sum = sum + tmp;
		}
		//如果字符是小寫字母
		else if ((a[x] >= 'A') && (a[x] <= 'F'))
		{
			b = a[x] - 'A' + 10;
			tmp = pow(16, n-1);
			tmp = tmp * b;
			sum = sum + tmp;
		}
		//否則爲不正確的字符輸入格式
		else
		{
			cout << "The addr is meaningless, please re-enter!";
			return 0;
		}
	}
	return sum;	
}


int main()
{
	int n,sum;
	string a;
	cout << "please enter register addr as Hex:"<<endl;
	cin >> a;
	n = a.size();
	sum=change(a, n);
	cout << "The addr's decimal is " << sum << endl;
	return 0;
}

C++11自帶函數

int main()
{
	int n,sum;
	string a;
	cout << "please enter register addr as Hex:"<<endl;
	cin >> a;
	n = std::stoi(a, nullptr, 16);
	cout << "The addr's decimal is " << n << endl;
	return 0;
}