Base Converter

#include <bits/stdc++.h>
using namespace std;
string str,nb;
int b,c;
char cn[10001];

char * Convert(int from,int to,const char * s,char * out)
{
    if(s==NULL)
        return NULL;
    if(from<2||from>36||to<2||to>36)
        return NULL;
    int il=strlen(s);
    int *fs=new int[il];
    int k=0;
    int i,j;
    for(i=il-1;i>=0;--i)
    {
        if(s[i]>='0'&&s[i]<='9')
        {
            fs[k]=(int)(s[i]-'0');
        }
        else
        {
            if(s[i]>='A'&&s[i]<='Z')
            {
                fs[k]=10+(int)(s[i]-'A');
            }
            else if(s[i]>='a'&&s[i]<='z')
            {
                fs[k]=10+(int)(s[i]-'a');
            }
            else
            {
                delete[]fs;
                return NULL;
            }
        }
        ++k;
    }
    for(i=0;i<il;++i)
    {
        if(fs[i]>=from )
            return NULL;
    }
    double x=ceil(log(from )/log (to));
    int ol=1+(il*x);
    int * ts=new int[ol];
    int * cums=new int [ol];
    for (i=0;i<ol;i++)
    {
        ts[i]=0;
        cums[i]=0;
    }
    ts[0]=1;
    for(i =0;i<il;++i)
    {
        for(j=0;j<ol;++j)
        {
            cums[j]+=ts[j]*fs[i];
            int temp=cums[j],rem=0,ip=j;
            do
            {
                rem=temp/to;
                cums[ip]=temp-rem*to;
                ++ip;
                if(ip>=ol)
                {
                    if(rem>0)
                    {
                        delete[]ts;
                        delete[]cums;
                        delete[]fs;
                        return NULL;
                    }
                    break;
                }
                cums[ip]+=rem;
                temp=cums[ip];
            }
            while (temp>=to);
        }
        for(j=0;j<ol;++j)
            ts[j]=ts[j]*from;
        for(j=0;j<ol;++j)
        {
            int temp=ts[j],rem=0,ip=j;
            do
            {
                rem=temp/to;
                ts[ip]=temp-rem*to;
                ++ip;
                if (ip >= ol)
                {
                    if (rem>0)
                    {
                        delete[]ts;
                        delete[]cums;
                        delete[]fs;
                        return NULL;
                    }
                    break;
                }
                ts[ip]+=rem;
                temp = ts[ip];
            }
            while(temp>=to);
        }
    }
    if(out==NULL )
        out=(char*)malloc(sizeof(char)*(ol+1));
    int spos=0;
    bool first=false;
    for(i=ol-1;i>=0;--i)
    {
        if (cums[i]!=0)
            first=true;
        if (!first)
            continue;
        if (cums[i]<10)
            out[spos]=(char)(cums[i]+'0');
        else
            out[spos]=(char)(cums[i]+'A'-10);
        ++spos;
    }
    out[spos]=0;
    delete[]ts;
    delete[]cums;
    delete[]fs;

    return out;
}

int main()
{
    ifstream f("base_converter.in");
    getline(f,str);
    f.close();
    vector<string>x;
    istringstream buffer(str);
    for(string w;buffer>>w;)
        x.push_back(w);
    for(unsigned int j=0;j<x.size();++j)
        switch(j)
        {
            case 0: nb=x[j];break;
            case 1: b=stoi(x[j]);break;
            case 2: c=stoi(x[j]);break;
        }
    int lnb=nb.length();
    char char_array[lnb+1];
    strcpy(char_array,nb.c_str());
    Convert(b,c,char_array,cn);
    ofstream g("base_converter.out");
    g<<cn;
    g.close();
    return 0;
}