: Converting Decimals to Hexadecimals,” gives a program that converts a decimal to a hexadecimal. How do you convert a hex number into a decimal?

#include <iostream>
#include<cmath>
#include<ctime>
#include<string>
#include <iomanip>
#include <fstream>

using namespace std;

int hexDec(const string& hex);
int hexCharToDecimal(char ch);
int main()
{
	cout << "enter a hex Number ";
	string hex;
	cin >> hex;

	cout << "The Decimal Number For Hex Is  " << hex
		<< " is " << hexDec(hex) << endl;
}
int hexDec(const string&  hex)
{
	int decimalValue = 0;
	for (unsigned i = 0; i < hex.length(); i++)
	{
		decimalValue = decimalValue * 16 + hexCharToDecimal(hex[i]);
	}
	return decimalValue;
	
}
int hexCharToDecimal(char ch)
{
	ch = toupper(ch);
	if (ch >= 'A' && ch <= 'F')
		return 10 + ch - 'A';
	else
		return ch - '0';
}