C storing strings into an array - c

Question

I'm working in a problem from the "C programming a Modern Approach 2nd Edition" text. I want to write a program that writes the smallest and largest words. The program stops accepting inputs when the user enters a 4-letter word.
I'm using an array of strings to solve this but I can't even get my program to store words in it.
#include <stdio.h>
#include <string.h>
#define WORD_LEN 20
int main()
{
char word[WORD_LEN]={0},ch;
char *a[10]={}; //Max 10 words in the array
int i=0,j;
for(;;)
{
printf("Enter a word: ");
fgets(word,WORD_LEN,stdin);
strtok(word, "\n"); //removes newline
a[i] = word;
if(strlen(word) == 4) //if word is 4 characters
break; //break out of loop
i++;
}
for(j=0;j<i;j++) //displaying array
printf("%s\n",a[j]);
return 0;
}
Output:
Enter a word: Analysis
Enter a word: Martin
Enter a word: Jonathan
Enter a word: Dana
Dana
Dana
Dana
Any idea into what I'm doing wrong? Thanks.

Answer 1

As BLUEPIXY mentioned, you are storing same address in all a[i]s. So at the end of the loop, it prints the last output i times.
Solution:
You need to allocate memory for a[i] and copy the strings.
#include <stdio.h>
#include <string.h>
#define WORD_LEN 20
#define MAX_NUM_WORD 10 //Max 10 words in the array
int main()
{
char word[WORD_LEN]={0},ch;
char *a[MAX_NUM_WORD]={0};
int i=0,j;
for(;;)
{
printf("Enter a word: ");
fgets(word,WORD_LEN,stdin);
strtok(word, "\n"); //removes newline
a[i] = malloc(sizeof(char)* (strlen(word)+1)); //1 for '\0'
strcpy(a[i], word);
i++;
if(strlen(word) == 4) //if word is 4 characters
break; //break out of loop
//i++; //You will be missing last 4 letter word if i++ is here.
if(MAX_NUM_WORD <= i) //You can store only MAX_NUM_WORD strings
break;
}
for(j=0;j<i;j++) //displaying array
printf("%s\n",a[j]);
//Your other code.
for(i=0; i<MAX_NUM_WORD && NULL != a[i]; i++)
free(a[i]); //Free the allocated memory.
return 0;
}

Answer 2

Adding to others answers, when using malloc to allocate memory for your strings, it is good to also check the return value of void* pointer returned from it.
Additionally, it is also safe to check the return value of fgets, just to be super safe.
This solution demonstrates these points:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define WORD_LEN 20
#define MAX_NUM_WORD 10
#define EXIT_LEN 4
int
main(void) {
char word[WORD_LEN];
char *a[MAX_NUM_WORD];
int i = 0, wrd;
while (i < MAX_NUM_WORD) {
printf("Enter a word: ");
if (fgets(word, WORD_LEN, stdin) != NULL) {
word[strlen(word)-1] = '\0';
}
a[i] = malloc(strlen(word)+1);
if (a[i] == NULL) {
fprintf(stderr, "%s\n", "Malloc Problem");
exit(EXIT_FAILURE);
}
strcpy(a[i], word);
i++;
if (strlen(word) == EXIT_LEN) {
break;
}
}
// Print and free, all at once.
for (wrd = 0; wrd < i; wrd++) {
printf("%s\n", a[wrd]);
free(a[wrd]);
a[wrd] = NULL;
}
return 0;
}