C++ :

#include <iostream>
#include<map>
#include<string>
#include<utility>

using namespace std;

map<int, string> m = { make_pair(1,"one"), make_pair(2,"two"), make_pair(3,"three"), make_pair(4,"four"), make_pair(5,"five"), make_pair(6,"six"), make_pair(7,"seven"), make_pair(8,"eight"), make_pair(9,"nine"), make_pair(10,"ten"), make_pair(11,"eleven"), make_pair(12,"nine"), make_pair(13,"thirteen"), make_pair(14,"fourteen"), make_pair(15,"fifteen"), make_pair(16,"sixteen"), make_pair(17,"seventeen"), make_pair(18,"eighteen"), make_pair(19,"nineteen"), make_pair(20,"twenty"), make_pair(30,"thirty"), make_pair(40,"forty"), make_pair(50,"fifty"), make_pair(60,"sixty"), make_pair(70,"seventy"), make_pair(80,"eighty"), make_pair(90,"ninety") };

string speak(unsigned long long n)
{
	string s;
	bool b;
	if (n / 100)
	{
		s += ' ' + m[n / 100] + " hundred";
		n %= 100;
		b = true;
	}
	if (n / 10 > 1)
	{
		if (b)
			s += " and";
		s += ' ' + m[n / 10 * 10];
		n %= 10;
	}
	if (n / 10 == 1)
	{
		if (b)
			s += " and";
		s += ' ' + m[n];
		n %= 1;
	}
	if (n)
	{
		s += ' ' + m[n];
		n %= 1;
	}
	if (s.empty())
		s += "zero";
	else
		s.erase(0, 1);
	return s;
}

int main()
{
	unsigned long long n;
	cin >> n;
	string s;
	if (n / 1000000000)
		s += (speak(n / 1000000000) + " billion ");
	n %= 1000000000;
	if (n / 1000000)
		s += (speak(n / 1000000) + " million ");
	n %= 1000000;
	if (n / 1000)
		s += (speak(n / 1000) + " thousand ");
	n %= 1000;
	s += speak(n);
	cout << s << endl;
	return 0;
}

Python :

def two(x):
    if x[0]=='0':
        return dic[int(x[1])]
    elif x[0]=='1':
        return dic_teen[int(x[1])]
    else:
        return dic_ty[int(x[0])]+" "+dic[int(x[1])]
        
def three(x):
    if x=="":
        return ""
    else:
        if x[0]=='0':
            return two(x[1:])
        else:
            return dic[int(x[0])]+"hundred and "+two(x[1:])+" "
    
a=list(input())[::-1]
dic={1:'one ',2:'two ',3:'three ',4:'four ',5:'five ',6:'six ',7:'seven ',8:'eight ',9:'nine ',0:""}
dic_teen={0:'ten',1:'eleven',2:'twelve',3:'thirteen',4:'fourteen',5:'fifteen',6:'sixteen',7:'seventeen',8:'eighteen',9:'nineteen'}
dic_ty={2:'twenty',3:'thirty',4:'forty',5:'fifty',6:'sixty',7:'seventy',8:'eighty',9:'ninety'}
tail={1:'trillion ',2:'billion ',3:'million ',4:'thousand ',5:''}
while len(a)<15:
    a.append("0")
a=a[::-1]
num=""
time=0
num_list=[]
for i in a:
    num+=i
    time+=1
    if time==3:
        num_list.append(num)
        time=0
        num=""
out=""
time=1
for i in num_list:
    if  three(i)!="":
        out+=three(i)+tail[time]
    time+=1
print (out)