Uva 389 - Basically Speaking

// 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>
#include<bitset>
#include<iomanip>
// 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 mset(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 s_wap(x,y) x^=y;y^=x;x^=y;
#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?gcd<T>(b,a%b):a;}
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;}

bool isChar(char cr)
{
    if(cr >='A' and cr <= 'Z')
    {
        return true;
    }
    else
    {
        return false;
    }
}

int get_hx(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;
    }
}

bool inIt(int k)
{
    if(k >=10 and k <=16)
    {
        return true;
    }
    else
    {
        return false;
    }
}

char retCh(int k)
{
    switch(k)
    {
    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;
    }
}

int main()
{
    string s;
    char ch[20+5];
    int base,tobase;

    while(cin >> s >> base >> tobase)
    {
        mset(ch,0);
        int len = s.size(),i,p=len-1,tke;
        LL res=0;

        for(i=0;i<len;i++)
        {
            if(isChar(s[i]))
            {
                tke = get_hx(s[i]);
            }
            else
            {
                tke = s[i]-48;
            }

            res += tke * powl(base,p);
            p--;
        }
        //cp(res);
        if(!res)
        {
            cout  << setw(7) << "0" << endl;
            continue;
        }
        int chlen=0,kp;
        char ca;

        while(res)
        {
            kp = res % tobase;
            //cp(kp);
            if(inIt(kp))
            {
                ch[chlen] = retCh(kp);
            }
            else
            {
                ch[chlen] = kp+48;
            }
            chlen++;
            res /= tobase;
        }
        //lp1(i,chlen)cp(ch[i]);
        if(chlen > 7)
        {
            cout << setw(7) << "ERROR" ;
        }
        else
        {
            string ans="";

            for(i=chlen-1;i>=0;i--)
            {
                ans+=(ch[i]);
            }

            cout << setw(7) << ans;
        }

        nl;
    }

    return 0;
}