exercise09.c

// C Primer Plus
// Chapter 12 

// Write a program with the following behavior. First, it asks you how many
// words you wish to enter. Then it has you enter the words, and then it
// displays the words. Use malloc() and the answer to the first question (the
// number of words) to create a dynamic array of the corresponding number of
// pointers-to-char. (Note that because each element in the array is a pointer-
// to-char, the pointer used to store the return value of malloc() should be a
// pointer-to-a-pointer-to-char.) When reading the string, the program should
// read the word into a temporary array of char, use malloc() to allocate
// enough storage to hold the word, and store the address in the array of char
// pointers. Then it should copy the word from the temporary array into the
// allocated storage. Thus, you wind up with an array of character pointers,
// each pointing to an object of the precise size needed to store the
// particular word. A sample run could look like this:
// 	> How many words do you wish to enter? 
//    5
//  > Enter 5 words now:
// 	  I enjoyed doing this exerise
// 	> Here are your words:
// 	  I 
//    enjoyed 
//    doing
//    this
//    exercise

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>

#define LIMIT 400

char ** get_words(int n);
static void find_word(char **start, char **end);

int main(void)
{
	int n;
	char ** words;

	printf("How many words do you wish to enter?\n");
	if (scanf("%d", &n) == 1 && n > 0)
	{
		while (getchar() != '\n')
			continue;
		words = get_words(n);

		printf("Here are your words:\n");
		for (int i = 0; i < n; i++)
			printf("%s\n", words[i]);
	}

	return 0;
}

char ** get_words(int n)
{
	char tmp[LIMIT];
	int i;
	char * word_start;
	char * word_end;
	int word_length;

	char ** word_array = (char **) malloc(n * sizeof(char *));

	printf("Enter %d words now:\n", n);
	word_start = fgets(tmp, LIMIT, stdin);

	for (i = 0; i < n; i++)
	{
		// find the start and end of next word
		find_word(&word_start, &word_end);
		
		// if word_start points to null char, there are no more
		// words to find; exit loop
		if (*word_start == '\0')
			break;

		// allocate memory for new word and copy from tmp
		word_length = word_end - word_start;
		word_array[i] = (char *) malloc((word_length + 1) * sizeof(char));
		if (word_array[i] != NULL)
		{
			strncpy(word_array[i], word_start, word_length);
			word_array[i][word_length] = '\0';
		}
		
		word_start = word_end;
	}

	// if less than n words found, set remaining elements of
	// word_array to null string
	if (i < n)
		for (; i < n; i++)
		{	
			word_array[i] = (char *) malloc(sizeof(char));
			*word_array[i] = '\0';
		}

	return word_array;
}

static void find_word(char **start, char **end)
{
	// takes two pointers to pointers to char
	// sets *start to point to first character of first
	// word occuring after **start and sets *end to point
	// to the character immediately after the word

	while (isspace(**start))
		(*start)++;

	*end = *start;

	while (!isspace(**end) && **end != '\0')
		(*end)++;
}