/*
  Name:    ex5-11.c
  Purpose: Display a two-digit number in English.
  Author:  Bill Slough

  Note:    The code is a bit tedious, though straightforward.
*/

#include <stdio.h>

void displayInEnglish(int n);
int numberOfDigits(int n);

int main() {
    int yourNumber;
    
    /* Get the input value */
    printf("Enter a two-digit number: ");
    scanf("%d", &yourNumber);

    if (yourNumber < 0 || numberOfDigits(yourNumber) != 2) {
        printf("A positive two-digit number was expected.\n");
        return 1;
    }
    else {
        printf("You entered the number ");
        displayInEnglish(yourNumber);
        printf(".\n");
    }
    return 0;
}

void displayInEnglish(int n) {
    /* Display a two-digit number in English

       Precondition:  n is a two-digit integer

       Result:  The appropriate English phrase corresponding to n is output.
    */

    if (n < 20) {
        /* values 10 through 19 are treated as a special case */          
        switch (n % 10) {
        case 0:
            printf("ten"); break;
        case 1:
            printf("eleven"); break;
        case 2:
            printf("twelve"); break;
        case 3:
            printf("thirteen"); break;
        case 4:
            printf("fourteen"); break;
        case 5:
            printf("fifteen"); break;
        case 6:
            printf("sixteen"); break;
        case 7:
            printf("seventeen"); break;
        case 8:
            printf("eighteen"); break;
        case 9:
            printf("nineteen"); break;
        }
        return;
    }
    
    /* for 20 through 99, output the tens digit value... */
    switch (n / 10) {
    case 2:                   
        printf("twenty"); break;
    case 3:
        printf("thirty"); break;
    case 4:
        printf("forty"); break;
    case 5:
        printf("fifty"); break;
    case 6:
        printf("sixty"); break;
    case 7:
        printf("seventy"); break;
    case 8:
        printf("eighty"); break;
    case 9:
        printf("ninety"); break;
    }

    /* ...followed by the value of the ones digit */
    switch (n % 10) {
    case 0:
        break;
    case 1:
        printf("-one"); break;
    case 2:
        printf("-two"); break;
    case 3:
        printf("-three"); break;
    case 4:
        printf("-four"); break;
    case 5:
        printf("-five"); break;
    case 6:
        printf("-six"); break;
    case 7:
        printf("-seven"); break;
    case 8:
        printf("-eight"); break;
    case 9:
        printf("-nine"); break;
    }
    return;
}

int numberOfDigits(int n) {
    /* How many digits does a given integer have?

       Precondition:  n is a non-negative integer

       Result:  returns the number of digits in n
    */
    int digits = 0;
    do {
        n /= 10;     /* remove the rightmost digit */
        digits++;    /* count it */
    } while (n > 0);

    return digits;
}