Base64Encode.cpp

#include <bits/stdc++.h>
#define f0(i,n) for(__typeof(n) i=0;i<n;i++)
#define rep(i,a,b) for(__typeof(b) i=a;i<=b;i++)
#define read(s) freopen(s , "r" ,stdin)
#define write(s) freopen(s , "w" , stdout)
#define BUG(x) cerr << #x << " = " << x << '\n'

using namespace std;

const string pattern = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";

string encode(string s){

	string res;

	f0(i,(int)s.length()){
		int k = (int)s[i];
		string tmp;
		f0(j,8){
			char cc;
			if (k & (1<<j)) cc = '1';
			else cc = '0';
			tmp.insert(tmp.begin(),cc);
		}
		res += tmp;
	}
	return res;
}

int main(){
	
	string s;
	string res;

	getline(cin,s);

	string tmp = encode(s);

	int remainder = 3 - (int)s.length() % 3;

	string add = "";

	if ( remainder < 3 ){
		f0(i,remainder) add += '=' , tmp += "00000000";
	
		f0(i,6*remainder) tmp.erase(tmp.end()-1);
	}

	for ( int i = 0 ; i < (int)tmp.length() ; i += 6 ){

		int num = 0;

		for ( int j = 5 ; j >= 0 ; j -- ) num |= ((int)(tmp[i+5-j]-'0'))<<j;

		res += pattern[num];
	}

	res += add;
	puts(res.c_str());
}