Displaying the contents of a dynamic array backwards - c

Question

So the program is supposed to do the following:
Ask the user to enter strings (max length of the string being 250), and once the user enters nothing (so basically hitting 'enter'), the program stops taking input and proceeds to display every string the user has input backwards.
Here's my code - everything works except I can't enter the while loop at the bottom.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
int main()
{
char userInput[250];
char *newSpace;
char *array;
int stringLength;
int inputElems = 0;
//Reset startingPtr back to where 'array' begins
char *startingPtr = array - inputElems;
// Sets endPtr to the last input element in the array
char *endPtr = startingPtr + inputElems;
do
{
puts("Please enter a string!");
// Gets input from user
fgets(userInput, 250, stdin);
// Finds out the number of characters the user entered
// + 1 to make room for the null character
stringLength = strlen(userInput) + 1;
// Allocate memory with the needed space
newSpace = malloc(stringLength);
// If malloc didn't allocate memory, display error
if (NULL == newSpace)
{
puts("Error!");
}
// Copy user input into array
strcpy(newSpace, userInput);
// Save input into array
array = newSpace;
// For testing purposes only, this line will be deleted once I can access the array
//puts("Here's what you wrote");
//printf("%s", array);
// Increase array
array++;
// Increase number of times user has input something
inputElems++;
} while(stringLength != 2);
//puts("Testing outside");
while (endPtr > startingPtr)
{
//puts("Testing inside");
--endPtr;
printf("%s", *endPtr);
}
free(newSpace);
}

Answer 1

Your while loop body is never executed because you never modify endPtr and startingPtr throughout the program's lifetime, they both point to the same location. Thus, endPtr > startingPtr will never be true.
Also, array++ does not work the way you expect: array points to the first character of what the user wrote, and array++ just moves it forward to the next character. I think you want an array of char *. Thus, change char *array; to char *array[250]; (assuming that the user can enter at most 250 sentences).
And of course, since you can't increment an array, because an array is not a modifiable l-value, you must also keep a count for the last index written. But I see that you already have inputElems, that should be enough. Here's the modified code:
int main()
{
char userInput[250];
char *newSpace;
char *array[250];
int stringLength;
int i;
int inputElems = 0;
do
{
puts("Please enter a string!");
// Gets input from user
fgets(userInput, 250, stdin);
// Finds out the number of characters the user entered
// + 1 to make room for the null character
stringLength = strlen(userInput) + 1;
// Allocate memory with the needed space
newSpace = malloc(stringLength);
// If malloc didn't allocate memory, display error
if (NULL == newSpace)
{
puts("Error!");
}
// Copy user input into array
strcpy(newSpace, userInput);
// Save input into array
array[inputElems] = newSpace;
// For testing purposes only, this line will be deleted once I can access the array
//puts("Here's what you wrote");
//printf("%s", array);
// Increase number of times user has input something
inputElems++;
} while(stringLength != 2);
//puts("Testing outside");
for (i = inputElems-1; i >= 0; i++)
{
//puts("Testing inside");
printf("%s", array[i]);
free(array[i]);
}
return 0;
}
Note the updated loop in the end of the code. It goes through the array from end to beginning. Note that I changed the place where you call free(). Since we're allocating memory inside a loop, for each position in array, we must also free() every position, thus this must also be made inside a loop.

Answer 2

Ok. you need an array of pointers like: char *arr[10];
You can store here 10 strings from arr[0] to arr[9]. (Well not directly 10 strings, but the pointers to them)
arr[0] = (char*)malloc(sizeof(char * length_of_string));
strncpy(arr[0], your_string, length_of_string);
When just print arr[9] to arr[0].
mfg