Question

I have the following code to populate an array of strings, but every time i change the value, the entire array changes (instead of a single string the array)

Answer 1

That’s because you are the same pointer to char for all positions of the array.

When you do:

words[i] = txt;

You are assigning a pointer. So every single word[i] is the same string (txt).
If you really want to read the word into a buffer (like txt) and then put it into the array of strings, you need to copy the contents of the buffer string to the string in the array, like so:

strncpy(words[i], txt, MAX_WORD_LENGTH);

There’s also another problem with your code, which is the allocation of the string array.
It should be:

words = (char**)malloc(wordcount * sizeof(char*));

That is because a string array is a pointer to a char pointer (char**), and each element of the array is a string (char*). Now you have allocated a array of char pointers, but you have not allocated the memory for each string, which is what we do next:

for (i = 0; i < wordcount; i++) {
    words[i] = (char*)malloc(MAX_WORD_LENGTH * sizeof(char));
}

If you want to not use a buffer and read directly into the string array, your code would be something like this:

words = (char**)malloc(wordcount * sizeof(char*));
input = fopen(filename, "r");
while(!feof(input)) {
    words[i] = (char*)malloc(MAX_WORD_LENGTH * sizeof(char));
    fscanf(input, "%s", words[i]);
}