Practice Assignment

(num2words.c)

Information

Write a program that prompts the user for a two-digit integer and then prints the English words for the number.
Here is the output from the program run interactively:
```
Enter a two-digit integer (10-99)? (0=quit) 22
twenty-two
Enter a two-digit integer (10-99)? (0=quit) 47
forty-seven
Enter a two-digit integer (10-99)? (0=quit) 99
ninety-nine
Enter a two-digit integer (10-99)? (0=quit) 50
fifty
Enter a two-digit integer (10-99)? (0=quit) 10
ten
Enter a two-digit integer (10-99)? (0=quit) 18
eighteen
Enter a two-digit integer (10-99)? (0=quit) 0
```
The program continues to run until the user types in 0 (zero) to terminate.
The name of the file should be num2words.c and the command to compile it will look like this:
```
gcc -Werror -Wall -Wextra -ansi -pedantic -O2 -Wno-unused-result -o num2words num2words.c main.c
```
Files:
- I am providing you with a driver (main.c: HTML Text) that will do the prompting. Your file (num2words.c) has one function in it and it is prototyped as such:
```
void number_to_words(int number);
```
  You only need to include one header file (stdio.h) in your file.
- Here is a sample input file and output file for you do diff with. Remember, using redirection will not show the actual numbers or provide a newline. The input file includes every number from 10 to 99, because that is all of the two-digit numbers.
  By the way, I didn't type those 91 numbers in the file. I was too lazy to type all of those numbers manually, so I wrote a simple program to create them instead. (See, we programmers are lazy!)

Notes

You don't have to worry about invalid input. Since my driver file is doing the prompting, you can assume that the number you are given is in the range 10-99.
Hint: There are kind of two things to print, and they are different. The first is the tens digit, the second is the ones digit. Print the tens digit first, then print the ones. So, if the number was 38, you would first print:
```
thirty
```
and then you would print:
```
-eight
```
The numbers from 10 to 19 are kind of unique and you should handle them separately. However you choose to do this: Do NOT have 90 separate if statements!!!! (Think before you start.) You will have several if...else if statements, so don't be alarmed.
Approximate number of lines of code: 60. That's because there are a lot of different cases to handle, so you'll have lots of if statements, but it's not that complicated.
To run the code non-interactively (redirecting input and output), you would do this:
```
num2words < input.txt > myoutput.txt
```
and then diff with the provided output.

This practice exercise is mostly testing your ability to use conditional statements such as if, else, and switch. You can decide whether you want to use if statments or the switch statement. I would recommend using both, just so you can practice them.

Advanced students: If you've already programmed before, you may know that this is more easily done with pointers and arrays, and you may want to use those. After you learn about pointers and arrays, I'll suggest that all students should re-code this program using those techniques. In fact, with pointers and arrays, you could handle 3-digit and 4-digit numbers easily with only a few if...else if statements.