Uva 10473 - Simple Base Conversion

 /// Header file begin
#include<iostream>
#include<cstdio>
#include<cstring>
#include<map>
#include<string>
#include<vector>
#include<cmath>
#include<cctype>
#include<sstream>
#include<set>
#include<list>
#include<stack>
#include<utility>
#include<queue>
#include<algorithm>
#include<cstdlib>
/// End
//..........
/// Macro
#define sf scanf
#define pf printf
#define lp1(i,n) for(i=0;i<n;i++)
#define lp2(i,n) for(i=1;i<=n;i++)
#define mem(c,v) memset(c,v,sizeof(c))
#define cp(a) cout<<" "<<a<<" "
#define nl puts("")
#define sq(x) ((x)*(x))
#define all(x) x.begin(),x.end()
#define reall(x) x.rbegin(),x.rend()
#define sz size()
#define gc getchar()
#define pb push_back
#define freader freopen("input.txt","r",stdin)
/// End.........

/// Size
#define mx7 20000100
#define mx6 1500000
#define mx5 100005
#define mx4 1000100
#define inf 1<<30                                           //infinity value
#define eps 1e-9
#define mx (65540)
#define mod 1000000007
#define pi acos(-1.0)

/// Macros for Graph

#define white 1
#define gray 2
#define black 3
#define nil 0

using namespace std;
/***************/

/// typedef

typedef long long LL;
typedef long L;
typedef unsigned long long ull;
typedef unsigned long ul;
typedef unsigned int ui;
typedef pair<int, int> pii;
typedef vector<int>vi;
typedef vector<long long> vll;
typedef vector<long>vl;
typedef vector<char>vch;
typedef vector<string>vs;
typedef map<int,int>mpii;
typedef map<int,bool>mpbi;
typedef map<long,bool>mpbl;
typedef map<long long,bool>mpbll;
typedef map<char,int>mpci;
typedef map<char,bool>mpbc;
typedef map<string,int>mpsi;
typedef map<long long,long long>mpll;

/// template

template<class T> T gcd(T a, T b ) {return b<=0?a:gcd(b,a%b);}
template<class T> T large(T a, T b ) {return a>b?a:b;}
template<class T> T small(T a, T b ) {return a<b?a:b;}
template<class T> T diffrnce(T a, T b) {return a-b<0?b-a:a-b;}

char H_D(LL num)
{
    switch(num)
    {
    case 10:
        return 'A';
        break;
    case 11:
        return 'B';
        break;
    case 12:
        return 'C';
        break;
    case 13:
        return 'D';
        break;
    case 14:
        return 'E';
        break;
    case 15:
        return 'F';
        break;

        default:
            break;
    }
}

int D_H(char ch)
{
    switch(ch)
    {
    case 'A':
        return 10;
        break;
    case 'B':
        return 11;
        break;
    case 'C':
        return 12;
        break;
    case 'D':
        return 13;
        break;
    case 'E':
        return 14;
        break;
    case 'F':
        return 15;
        break;

    default:
        break;
    }
}

int main()
{
    string s;
    vi v;

    while(cin >> s)
    {
        if(s[0]=='-') break;

        LL ans=0,i,p,len;
        v.clear();

        // hexa-decimal to decimal

        if( (s[0]=='0' or s[0]=='O') and s[1]=='x')
        {
            ans = 0;

            len = s.size();

            for(i=2;i<len;i++)
            {
                if(isalpha(s[i]))
                {
                    v.push_back(D_H(s[i]));
                }

                else
                {
                    v.push_back(s[i]-48);
                }
            }

            LL vlen=v.size();
            p=vlen-1;

            for(i=0;i<vlen;i++)
            {
                ans+=v[i]*powl(16,p);
                p--;
            }

            pf("%lld\n",ans);
        }

        // decimal to hexa-decimal

        else
        {
            ans=0;
            len=s.size();
            p=len-1;

            for(i=0;i<len;i++)
            {
                ans+=(s[i]-48)*powl(10,p);
                p--;
            }

            LL a=ans;

            while(ans>0)
            {
                a=ans%16;
                v.push_back(a);
                ans/=16;
            }

            reverse(all(v));

            LL vlen=v.size();
            p=0,ans=0;

            pf("0x");

            for(i=0;i<vlen;i++)
            {
                if(v[i]<10)
                {
                    pf("%d",v[i]);
                }

                else
                {
                    pf("%c",H_D(v[i]));
                }
            }

            nl;
        }
    }

    return 0;
}