c++ program to convert number into words not working

Question

Here is a program written in c++ from this Write code to convert given number into words (eg 1234 as input should output one thousand two hundred and thirty four) question I modified to convert number into words.

In my program, instead of repeated using cout, I created an ostream object out and placed the return value in out.

Here is the program

#include<iostream>
using namespace std;
ostream & expand(int);
int main()
{
    int num;
    cin>>num;

   cout<<expand(num);
}
ostream & expand(int value)
{
ostream   &out;
out<<"";
    const char * const ones[21] = {"zero", "one", "two", "three","four","five","six","seven",
    "eight","nine","ten", "eleven","twelve","thirteen","fourteen","fifteen","sixteen","seventeen",
    "eighteen","nineteen"};
    const char * const tens[10] = {"", "ten", "twenty", "thirty","forty","fifty","sixty","seventy",
    "eighty","ninety"};

    if(value<0)
    {
        out<<"minus "<<expand(-value);

    }
else if(value>=1000000){
out<<expand(value/1000000)<<" million";
if(value % 1000000)
{
out<<" "<<expand(value % 1000000);
}

}
    else if(value>=1000)
    {
        out<<expand(value/1000)<<" thousand";

        if(value % 1000)
        {
            if(value % 1000 < 100)
            {
                out << " and";
            }
            out << "  " <<expand(value % 1000);
        }
    }
    else if(value >= 100)
    {
        out<<expand(value / 100)<<" hundred";

        if(value % 100)
        {
            out << " and "<<expand (value % 100);
        }
    }
    else if(value >= 20)
    {
        out << tens[value / 10];
        if(value % 10)
        {
            out << " " << expand(value % 10);
        }
    }
    else
    {
        out << ones[value];
    }
    return &out;
}

However, I get the following error while compiling.

In function 'std::ostream& expand(int)':
Line 13: error: 'out' declared as reference but not initialized
compilation terminated due to -Wfatal-errors.

Please help me.

I tried setting ostream &out=cout; and at the end return out. But I get the following result for cout<<expand(111234).

one0x8050884 hundredeleven and 0x80508840x8050884 thousandtwo0x8050884 hundredthirtyfour 0x8050884 and 0x8050884 0x80508840x8050884

Answer 1

ostream   &out; // Error

You must initialize out by an object. Because references always must refer to something.

ostream   &out = cout;

Answer 2

The problem is here:

ostream   &out;

As the compiler is telling you, references must be initialized. They cannot be default-constructed. Per Paragraph 8.3.5/1 of the C++11 Standard:

A variable declared to be a T& or T&&, that is, “reference to type T” (8.3.2), shall be initialized by an object, or function, of type T or by an object that can be converted into a T.

If you meant to bind out to the standard output, then you could do this:

ostream& out = std::cout;

Alternatively, you could make out a parameter of your function, binding to std::cout by default:

ostream& expand(int value, ostream& out = std::cout)
{
    out << "";
    // ...
}

This way, clients can call expand() and let it output to a specified stream (e.g. an std::ostringstream or an std::ofstream), or to the standard output if no stream is specified.

Answer 3

If you want to chain output like that, you should use the method given in Andy's answer. Currently, the system is trying to output your ostream pointer as a value, it's not able to chain properly as you don't supply the stream as an input parameter.

Answer 4

#include<stdio.h>
#include<conio.h>

void two_dgt(int);
void three_dgt(int);   //Function Declarations
void four_dgt(int);
long int num,hd_place,th_place;
char single[10][6] = {"","one","two","three","four",
        "five","six","seven","eight","nine"};

char tens_multi[10][8] = {"","ten","twenty","thirty","forty",
        "fifty","sixty","seventy","eighty","ninety"};

char dual[10][10] = {"ten","eleven","twelve","thirteen","fourteen",
         "fifteen","sixteen","seventeen","eighteen","nineteen"};

void main()
{
   clrscr();
   printf("Enter the number upto 5 digits: ");
   scanf("%ld",&num);
   if(num == 0)
     printf("Zero");
   else
   {
       clrscr();
       printf("\n\nEntered number: %ld",num);
       printf("\nIn words:       ");
       if(num < 10)
          printf("%s",single[num]); //use to print single digit number
       else if(num < 100)
          two_dgt(num);          //call a function to print two digits
       else if(num < 1000)
          three_dgt(num);      //call a function to print three digits
       else if(num < 10000)
          four_dgt(num);        //call a function to print four digits
       else if(num < 100000)
       {
          th_place = num/1000;
          two_dgt(th_place);
          printf(" thousand ");
          num = num - (th_place*1000);
          hd_place = num/100;
          if(hd_place == 0)
              two_dgt(num);
          else
              three_dgt(num);
       }
       else if(num > 99999)
       {
          clrscr();
          printf("\nError: number range should be upto 5 digits");
        }     
    }
    getch();

}

void two_dgt(int num)
{
if(num%10 == 0)
  printf("%s",tens_multi[num/10]);
else
{
  if(num/10 == 1)
     printf("%s",dual[num%10]);
  else
     printf("%s %s",tens_multi[num/10],single[num%10]);
}
}

void three_dgt(int num)
{
 hd_place = num/100;
 printf("%s hundred ",single[hd_place]);
 num = num - (hd_place*100);
 two_dgt(num);
}

void four_dgt(int num)
{
  th_place = num/1000;
  printf("%s thousand ",single[th_place]);
  num = num - (th_place*1000);
  hd_place = num/100;
  if(hd_place == 0)
     two_dgt(num);
  else
     three_dgt(num);
 }