Display english name of a given number

#include <iostream>
#include <string>
#include <iomanip>
using namespace std;

//Function name: dig1
//Purpose: Prints the english version of the last digit of the original number
//Parameters: The last digit of the original number
//Return value: None
void dig1(int a)
{
    if (a == 0) {
        cout << endl;
    }
    else if (a == 1) {
        cout << "ONE" << endl;
    }
    else if (a == 2) {
        cout << "TWO" << endl;
    }
    else if (a == 3) {
        cout << "THREE" << endl;
    }
    else if (a == 4) {
        cout << "FOUR" << endl;
    }
    else if (a == 5) {
        cout << "FIVE" << endl;
    }
    else if (a == 6) {
        cout << "SIX" << endl;
    }
    else if (a == 7) {
        cout << "SEVEN" << endl;
    }
    else if (a == 8) {
        cout << "EIGHT" << endl;
    }
    else if (a == 9) {
        cout << "NINE" << endl;
    }
}
//Function name: dig2
/*Purpose: Prints the english version of the 3rd digit of the original number. If the 3rd digit is 1, prints the word associated with 1 and the last
 digit. Also sends the value of the last digit to dig1.*/
//Parameters: The last two digits of the original number
//Return value: None
void dig2(int c)
{
    int a = c / 10;
    int b = c % 10;
    if (a == 0) {
        dig1(b);
    }
    else if (a == 1) {
        if (b == 0) {
            cout << "TEN" << endl;
        }
        else if (b == 1) {
            cout << "ELEVEN" << endl;
        }
        else if (b == 2) {
            cout << "TWELVE" << endl;
        }
        else if (b == 3) {
            cout << "THIRTEEN" << endl;
        }
        else if (b == 4) {
            cout << "FOURTEEN" << endl;
        }
        else if (b == 5) {
            cout << "FIFTEEN" << endl;
        }
        else if (b == 6) {
            cout << "SIXTEEN" << endl;
        }
        else if (b == 7) {
            cout << "SEVENTEEN" << endl;
        }
        else if (b == 8) {
            cout << "EIGHTEEN" << endl;
        }
        else if (b == 9) {
            cout << "NINETEEN" << endl;
        }
    }
    else if (a == 2) {
        cout << "TWENTY ";
        dig1(b);
    }
    else if (a == 3) {
        cout << "THIRTY ";
        dig1(b);
    }
    else if (a == 4) {
        cout << "FOURTY ";
        dig1(b);
    }
    else if (a == 5) {
        cout << "FIFTY ";
        dig1(b);
    }
    else if (a == 6) {
        cout << "SIXTY ";
        dig1(b);
    }
    else if (a == 7) {
        cout << "SEVENTY ";
        dig1(b);
    }
    else if (a == 8) {
        cout << "EIGHTY ";
        dig1(b);
    }
    else if (a == 9) {
        cout << "NINETY ";
        dig1(b);
    }
}
//Function name: dig3
//Purpose: Prints the english version of the 2nd digit of the original number. Also sends the value of the last 2 digits to dig2.
//Parameters: The last three digits of the original number
//Return value: None
void dig3(int c)
{
    int a = c / 100;
    int b = c % 100;
    if (a == 0) {
        dig2(b);
    }
    else if (a == 1) {
        cout << "ONE HUNDRED ";
        dig2(b);
    }
    else if (a == 2) {
        cout << "TWO HUNDRED ";
        dig2(b);
    }
    else if (a == 3) {
        cout << "THREE HUNDRED ";
        dig2(b);
    }
    else if (a == 4) {
        cout << "FOUR HUNDRED ";
        dig2(b);
    }
    else if (a == 5) {
        cout << "FIVE HUNDRED ";
        dig2(b);
    }
    else if (a == 6) {
        cout << "SIX HUNDRED ";
        dig2(b);
    }
    else if (a == 7) {
        cout << "SEVEN HUNDRED ";
        dig2(b);
    }
    else if (a == 8) {
        cout << "EIGHT HUNDRED ";
        dig2(b);
    }
    else if (a == 9) {
        cout << "NINE HUNDRED ";
        dig2(b);
    }
}
//Function name: dig4
//Purpose: Prints the english version of the 1st digit of the original number. Also sends the value of the last 3 digits to dig3.
//Parameters: The original number
//Return value: None
void dig4(int c)
{
    int a = c / 1000;
    int b = c % 1000;
    if (a == 0) {
        dig3(b);
    }
    else if (a == 1) {
        cout << "ONE THOUSAND ";
        dig3(b);
    }
    else if (a == 2) {
        cout << "TWO THOUSAND ";
        dig3(b);
    }
    else if (a == 3) {
        cout << "THREE THOUSAND ";
        dig3(b);
    }
    else if (a == 4) {
        cout << "FOUR THOUSAND ";
        dig3(b);
    }
    else if (a == 5) {
        cout << "FIVE THOUSAND ";
        dig3(b);
    }
    else if (a == 6) {
        cout << "SIX THOUSAND ";
        dig3(b);
    }
    else if (a == 7) {
        cout << "SEVEN THOUSAND ";
        dig3(b);
    }
    else if (a == 8) {
        cout << "EIGHT THOUSAND ";
        dig3(b);
    }
    else if (a == 9) {
        cout << "NINE THOUSAND ";
        dig3(b);
    }
}
int main()
{
    int number;
    int c = 0;
    while (c < 1) {
        cout << "Enter a number between 0 and 9999." << endl;
        cin >> number;
        if (number >= 0 && number <= 9999) {
            if (number == 0) {
                cout << "ZERO" << endl;
                break;
            }
            else if (number > 0 && number < 10) {
                dig1(number);
                break;
            }
            else if (number >= 10 && number < 100) {
                dig2(number);
                break;
            }
            else if (number >= 100 && number < 1000) {
                dig3(number);
                break;
            }
            else if (number >= 1000 && number < 10000) {
                dig4(number);
                break;
            }
        }
        else {
            cout << "You did not enter a number between 0 and 9999." << endl;
        }

    }
    return 0;
}