Adding a number to a word to call up a variable - c++

Question

Please be nice I am a total newby.
I have a list of variables (strings) from num1 to num90. I need to call these from a function by adding the number in an int to the word num.
The task is to convert digits to words from 'jumping into c++'...I might not be going about it in the 'right' way but this part has been stopping me for a while now!!
I'm trying like this:
#include <iostream>
#include <string>
using namespace std;
// Hard code numbers to 20 and then in tens to 90
string num1 = "one";
string num2 = "two";
string num3 = "three";
string num4 = "four";
string num5 = "five";
string num6 = "six";
string num7 = "seven";
string num8 = "eight";
string num9 = "nine";
Etc...up to 90
int main ()
{
// Break the number down into three digit blocks
int num = 0;
cout << "Please enter the number: ";
cin >> num;
while (num > 999)
{
int digit = (num % 1000);
num = ((num - digit)/1000);
//cout << digit << '\n';
//cout << num << '\n';
// For each block of numbers work out hundreds,
if (digit > 100)
{
int i = digit;
int j = (i % 100);
cout << num.append(j) << " hundred";
}
What I need to happen is the number stored in 'j' to be tagged onto the word num in order to call the string num*.
Is this possible?

Answer 1

Sure, use a map:
#include <map>
#include <string>
#include <iostream>
std::map<int, std::string> words { { 1, "one" }, { 2, "two" }, { 3, "three" } };
int main()
{
std::cout << words[1] << std::endl;
}
You'll probably have to deal with some special cases (up to twenty?), and you need a word for "hundred", etc. If you want to make it internationalizable, you'll have to think even harder.

Answer 2

What I need to happen is the number stored in 'j' to be tagged onto
the word num in order to call the string num*.
The trouble with that approach is that any variable names you use in your code are not compiled: when the program runs it will manipulate the values of your variables, but it doesn't know or care that you decided to use the name "num3" instead of "numero3" or "foobar".
If you want to make a link between a digit (3) and a string ("three") then you can use a Vector (as #Mark suggests, although you'll have problems after 20) or better still a Map (as #Kerrek suggests): these will work because in both cases the strings are referenced by the value of a variable (eg the value of digit in lookup[digit], or the literal value 1 in words[1]) rather than by the name of a variable.
EDIT:
For interest, here's a version using 'if' and 'switch'...
#include <iostream>
#include <string>
using namespace std;
string units2word(int units){
switch (units){
case 0: return "zero";
case 1: return "one";
case 2: return "two";
case 3: return "three";
// etc ...
case 18: return "eighteen";
case 19: return "nineteen";
}
}
string tens2word(int tens){
switch(tens){
case 2: return "twenty";
case 3: return "thirty";
// etc ...
case 9: return "ninety";
}
}
string num2words(int num) {
if (num > 99 && num%100 == 0) return units2word(num/100) + " hundred";
if (num > 99) return units2word(num/100) + " hundred and " + num2words(num%100);
if (num < 20) return units2word(num);
if (num%10 == 0) return tens2word(num/10);
return tens2word(num/10) +"-"+ units2word(num%10);
}
int main(int argc, char *argv[]) {
int num = -1;
while( num < 0 || num > 999){
cout << "Please enter a number between 0 and 999: ";
cin >> num;
}
cout << "You typed: " << num2words(num) << endl;
}

Answer 3

You should look at using std::vector. This gives you a variable that takes an index
std::vector<std::string> lookup;
lookup.push_back( "zero" ); // starts at lookup[0]
lookup.push_back( "one" );
lookup.push_back( "two" );
// etc
// then
std::cout << lookup[digit] << std::endl;
std::cout << lookup[num] << std::endl;