#include <stdio.h>
#include <math.h>

#define ARRAYSIZE 1000
using namespace std;
int htol(char s[]);

int main()
{
        char userNumber[ARRAYSIZE];

        printf("Enter hexadecimal number: ");
        gets_s(userNumber);
        printf("Decimal number: %d", htol(userNumber));
		getchar();
        return 0;
}

int htol(char s[])
{
    int i, length, sum = 0;

    for(length = 0; s[length] != '\0'; ++length);

    for(i = 0; s[i] != '\0'; ++i, --length)
    {
        if(s[i] >= '0' && s[i] <= '9')
			sum += (s[i] - '0') * powf(16,length-1);
        if(s[i] >= 'A' && s[i] <= 'F')
            sum += (s[i] - 55) * powf(16, length-1);
        if(s[i] >= 'a' && s[i] <= 'f')
            sum +=(s[i] - 87) * powf(16, length-1);
    }

    return sum;
}