C++ program to convert hexadecimal to decimal

dz1_v4.cpp

// C++ program to convert hexadecimal to decimal
#include <iostream>
#include <string.h>
#include <cmath>
using namespace std;

// Function to validate input data
int validateInput(string hexVal)
{
	int result = 0;
	int len = hexVal.size();
	if (len < 1) {
		cout << "Empty input?\n";
		result = 0;
	} else {
		result = 1;
	}
	
	// now validate every symbol of the line
	for (int i=0; i<len; i++) {
		// convert to uppercase for further operation with uppercase
		hexVal[i] = toupper(hexVal[i]);
		//cout << hexVal[i];
		if (!(((floor(hexVal[i]) == ceil(hexVal[i])) /* check if is integer */
				&& (hexVal[i] >= '0' && hexVal[i] <= '9')) /* if is integer, check value */
			|| ((isalpha(hexVal[i])) /* if is a latin letter  */
				&& (hexVal[i] >= 'A' && hexVal[i] <= 'F')) )) { /* check that it is A-F */
					cout << hexVal[i] << " is an invalid character for a hexademical number!\n";
					result = 0;
					break;
			}
	}
	
	return result;
}

// Function to convert hexadecimal to decimal
int hexadecimalToDecimal(string hexVal)
{
	int len = hexVal.size();

	// Initializing base value to 1, i.e 16^0
	int base = 1;

	int dec_val = 0;

	// Extracting characters as digits from last character
	for (int i=len-1; i>=0; i--)
	{
		// if character lies in '0'-'9', converting
		// it to integral 0-9 by subtracting 48 from
		// ASCII value.
		if (hexVal[i]>='0' && hexVal[i]<='9')
		{
			dec_val += (hexVal[i] - 48)*base;

			// incrementing base by power
			base = base * 16;
		}

		// if character lies in 'A'-'F' , converting
		// it to integral 10 - 15 by subtracting 55
		// from ASCII value
		else if (hexVal[i]>='A' && hexVal[i]<='F')
		{
			dec_val += (hexVal[i] - 55)*base;

			// incrementing base by power
			base = base*16;
		}
	}

	return dec_val;
}

int main()
{
	string hexNum;
	cout << "Enter input number:\n";
	getline(cin, hexNum);
	if (!validateInput(hexNum)) {
		cout << "Error\n";
		return 1;
	} else {
		cout << hexadecimalToDecimal(hexNum) << endl;
	}
}