word scramble with pointers in an array. Crashes when run - c

Question

I am new to arrays with pointers, and I am trying to make an array of pointers word scramble game that allows 3 tries to guess the word before the game ends. Basically, I have created a function that scrambles a string. Then, that string is sent to a new string, which is shown to the user. The user then enters their guess. I am getting no signal from my compiler on what is wrong.. It just crashes when it is run. I believe the error is when I am sending the pointer to the method. Could someone please tell me why this error is happening? Thanks.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <ctype.h>
void scramble(char *strings)
{
int length = strlen(strings), i, randomNum;
char temp;
for(i = 0; i < length/2; i++)
{
randomNum = rand()%length;
temp = strings[i];
strings[i] = strings[length - randomNum];
strings[length - randomNum] = temp;
}
}
int main()
{
int i, tries, NUMWORDS;
char *words[] = { "pumpkin", "cantalope", "watermelon", "apple", "kumquat" };
char *scramWords, *user;
NUMWORDS = strlen(words);
srand(time(NULL));
for(i = 0; i < NUMWORDS; i++)
{
scramWords[i] = words[i];
scramble(scramWords[i]);
}
printf("How to play: You get 3 tries to guess each scrambled word.\n");
for(i = 0; i < NUMWORDS; i++)
{
tries = 0;
while(tries !=4)
{
if(tries == 3)
{
printf("You Lose\n");
return 0;
}
printf("Unscramble: %s\n", scramWords[i]);
gets(user);
if(strcmp(user, words[i]) == 0)
{
printf("Correct!\n");
break;
}
else
{
tries++;
}
}
}
printf("You Win!");
return 0;
}

Answer 1

You must not try to modify string literals, or you will invoke undefined behavior. Copy strings before editing them instead of just assigning pointers.
length - randomNum may be length when randomNum is 0.
strlen(words) won't be the number of elements in words. You can use sizeof(words) / sizeof(*words).
You must allocate some buffer to scramWords and user before writing anything there.
You shouldn't use gets(), which has unavoidable risk of buffer overrun, deprecated in C99 and removed from C11.
Try this:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <time.h>
#include <ctype.h>
void scramble(char *strings)
{
int length = strlen(strings), i, randomNum;
char temp;
for(i = 0; i < length/2; i++)
{
randomNum = rand()%length;
temp = strings[i];
strings[i] = strings[length - randomNum - 1];
strings[length - randomNum - 1] = temp;
}
}
int main(void)
{
int i, tries, NUMWORDS;
char *words[] = { "pumpkin", "cantalope", "watermelon", "apple", "kumquat" };
char **scramWords, user[1024], *lf;
NUMWORDS = sizeof(words) / sizeof(*words);
srand(time(NULL));
scramWords = malloc(sizeof(*scramWords) * NUMWORDS);
if(scramWords == NULL)
{
perror("malloc");
return 1;
}
for(i = 0; i < NUMWORDS; i++)
{
scramWords[i] = malloc(strlen(words[i]) + 1); /* +1 for terminating null-character */
if(scramWords[i] == NULL)
{
perror("malloc");
return 1;
}
strcpy(scramWords[i], words[i]);
scramble(scramWords[i]);
}
printf("How to play: You get 3 tries to guess each scrambled word.\n");
for(i = 0; i < NUMWORDS; i++)
{
tries = 0;
while(tries !=4)
{
if(tries == 3)
{
printf("You Lose\n");
return 0;
}
printf("Unscramble: %s\n", scramWords[i]);
if(fgets(user, sizeof(user), stdin) == NULL)
{
puts("fgets failed");
return 1;
}
if((lf = strchr(user, '\n')) != NULL)
{
*lf = '\0'; /* remove newline character after string read */
}
if(strcmp(user, words[i]) == 0)
{
printf("Correct!\n");
break;
}
else
{
tries++;
}
}
}
printf("You Win!");
return 0;
}

Answer 2

you have a few issues in your code:
1), scramblegets a char * but here
scramWords[i] = words[i];
scramble(scramWords[i]);
you provide it with a char so define your scramWords as a char** instead of char*
2) You don't allocate space when declaring a pointer - that could lead to segfault. Use malloc or before accessing the pointer.
3) When assigning strings from one pointer to another use strcpy, not = operator
4) Use sizeof(words)/sizeof(*words) instead of NUMWORDS = strlen(words);
That should leave you with a working piece of code, but, as said in comments - take care of your warnings!