Task: Four is magic

C: #include <stdint.h>
#include <stdio.h>
#include <glib.h>

typedef struct named_number_tag {
    const char* name;
    uint64_t number;
} named_number;

const named_number named_numbers[] = {
    { "hundred", 100 },
    { "thousand", 1000 },
    { "million", 1000000 },
    { "billion", 1000000000 },
    { "trillion", 1000000000000 },
    { "quadrillion", 1000000000000000ULL },
    { "quintillion", 1000000000000000000ULL }
};

const named_number* get_named_number(uint64_t n) {
    const size_t names_len = sizeof(named_numbers)/sizeof(named_number);
    for (size_t i = 0; i + 1 < names_len; ++i) {
        if (n < named_numbers[i + 1].number)
            return &named_numbers[i];
    }
    return &named_numbers[names_len - 1];
}

size_t append_number_name(GString* str, uint64_t n) {
    static const char* small[] = {
        "zero", "one", "two", "three", "four", "five", "six", "seven", "eight",
        "nine", "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen",
        "sixteen", "seventeen", "eighteen", "nineteen"
    };
    static const char* tens[] = {
        "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"
    };
    size_t len = str->len;
    if (n < 20) {
        g_string_append(str, small[n]);
    }
    else if (n < 100) {
        g_string_append(str, tens[n/10 - 2]);
        if (n % 10 != 0) {
            g_string_append_c(str, '-');
            g_string_append(str, small[n % 10]);
        }
    } else {
        const named_number* num = get_named_number(n);
        uint64_t p = num->number;
        append_number_name(str, n/p);
        g_string_append_c(str, ' ');
        g_string_append(str, num->name);
        if (n % p != 0) {
            g_string_append_c(str, ' ');
            append_number_name(str, n % p);
        }
    }
    return str->len - len;
}

GString* magic(uint64_t n) {
    GString* str = g_string_new(NULL);
    for (unsigned int i = 0; ; ++i) {
        size_t count = append_number_name(str, n);
        if (i == 0)
            str->str[0] = g_ascii_toupper(str->str[0]);
        if (n == 4) {
            g_string_append(str, " is magic.");
            break;
        }
        g_string_append(str, " is ");
        append_number_name(str, count);
        g_string_append(str, ", ");
        n = count;
    }
    return str;
}

void test_magic(uint64_t n) {
    GString* str = magic(n);
    printf("%s\n", str->str);
    g_string_free(str, TRUE);
}

int main() {
    test_magic(5);
    test_magic(13);
    test_magic(78);
    test_magic(797);
    test_magic(2739);
    test_magic(4000);
    test_magic(7893);
    test_magic(93497412);
    test_magic(2673497412U);
    test_magic(10344658531277200972ULL);
    return 0;
}





Java: public class FourIsMagic {

    public static void main(String[] args) {
        for ( long n : new long[] {6, 60, 89, 300, 670, 2000, 2467, 20000, 24500,200000, 230000, 246571, 2300000, 2465712, 20000000, 24657123, 230000000, 245000000, -246570000, 123456789712345l, 8777777777777777777L, Long.MAX_VALUE}) {
            String magic = fourIsMagic(n);
            System.out.printf("%d = %s%n", n, toSentence(magic));
        }
    }
    
    private static final String toSentence(String s) {
        return s.substring(0,1).toUpperCase() + s.substring(1) + ".";
    }
    
    private static final String[] nums = new String[] {
            "zero", "one", "two", "three", "four", "five", "six", "seven", "eight", "nine", 
            "ten", "eleven", "twelve", "thirteen", "fourteen", "fifteen", "sixteen", "seventeen", "eighteen", "nineteen"
    };
    
    private static final String[] tens = new String[] {"zero", "ten", "twenty", "thirty", "forty", "fifty", "sixty", "seventy", "eighty", "ninety"};

    private static final String fourIsMagic(long n) {
        if ( n == 4 ) {
            return numToString(n) + " is magic";
        }
        String result = numToString(n);
        return result + " is " + numToString(result.length()) + ", " + fourIsMagic(result.length());
    }
    
    private static final String numToString(long n) {
        if ( n < 0 ) { 
            return "negative " + numToString(-n);
        }
        int index = (int) n;
        if ( n <= 19 ) {
            return nums[index];
        }
        if ( n <= 99 ) {
            return tens[index/10] + (n % 10 > 0 ? " " + numToString(n % 10) : "");
        }
        String label = null;
        long factor = 0;
        if ( n <= 999 ) {
            label = "hundred";
            factor = 100;
        }
        else if ( n <= 999999) {
            label = "thousand";
            factor = 1000;
        }
        else if ( n <= 999999999) {
            label = "million";
            factor = 1000000;
        }
        else if ( n <= 999999999999L) {
            label = "billion";
            factor = 1000000000;
        }
        else if ( n <= 999999999999999L) {
            label = "trillion";
            factor = 1000000000000L;
        }
        else if ( n <= 999999999999999999L) {
            label = "quadrillion";
            factor = 1000000000000000L;
        }
        else {
            label = "quintillion";
            factor = 1000000000000000000L;
        }
        return numToString(n / factor) + " " + label + (n % factor > 0 ? " " + numToString(n % factor ) : "");
    }

}