Thread: Using dynamically allocated strings to sort words

Here are the instructions:

Write a program that sorts a series of words entered by the user:

Enter word: foo
Enter word: bar
Enter word: baz
Enter word: quux
Enter word:

In sorted order: bar baz foo quux

Assume that each word is no more than 20 characters long. Assume there are no more than 50 words to be sorted. Stop reading when the user enters an empty word (i.e., press Enter without entering a word). Store each word in a dynamically allocated string, using an array of pointers to keep track of the strings. After all the words have been read, sort the array and then print the words in a sorted order.

Hint:
1) Use the read_line function (textbook, page 287 or slide 20, July 2 lecture) to read each word.
2) Use qsort function in <stdlib.h> to sort an array of strings.

I have been getting the following error and warning when I attempt to compile:

sort_words.c:18: error: invalid operands to binary *
sort_words.c:30: warning: comparison between pointer and integer

Where exactly did I go wrong? What do I have to do to get the words to sort in order?

Code:

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#define WORD_LEN 50
#define WORD_LIMIT 20

int read_line(char str[], int n);

int int_compare(const void* p, const void* q);

int main()
{
char n[WORD_LIMIT];
int i;
int *a;

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

for(i = 0; i < WORD_LEN; i++)
{
printf("Enter a word: ");
scanf("%c", &n[i]);
} 

qsort(n, WORD_LEN, sizeof(char), int_compare);

printf("In sorted order:\n");

for(i = 0; i < n; i++)
printf("%c\t", a[i]);

printf("\n");

return 0;
}

int int_compare(const void* p, const void* q){

int n1 = *(int *) p;
int n2 = *(int *) q;

if (n1 < n2)
return -1;

if (n1 == n2)
return 0;

return 1;
}



int read_line(char str[], int n)
{
int ch, i = 0;
while ((ch = getchar()) != '\n') {
if (i < n)
str[i++] = ch;
}
str[i] = '\0';
return i;
}

This is incorrect as well:

Code:

 printf("Enter a word: ");
 scanf("%c", &n[i]);     /* n alone will suffice here no need for '&' */

Also in looking at this a bit closer what you need is two demensional array allocation. You need to dynamically allocate for

Code:

For instance:

int **a = mallocMy2dArray(WORD_LIMIT, WORD_LEN);

 ...

int **mallocMy2dArray(int WLim, int Wlen)
{

  your code here to accomplish this

}

Also are you expecting your users to try typing in WORD_LEN number of words, this is what your for loop is doing.

Originally Posted by slingerland3g

Also in looking at this a bit closer what you need is two demensional array allocation. You need to dynamically allocate for

Code:

For instance:

int **a = mallocMy2dArray(WORD_LIMIT, WORD_LEN);

 ...

int **mallocMy2dArray(int WLim, int Wlen)
{

  your code here to accomplish this

}

Also are you expecting your users to try typing in WORD_LEN number of words, this is what your for loop is doing.

Nah, he just needs to make the n[WORD_LIMIT] be a *n[WORD_LIMIT]. Why over complicate the matter?