Here I have a string:

*line = "123 567 890  ";

with 2 spaces at the end. I wish to add those 2 spaces to 3's end and 7's end to make it like this:

"123  567  890"

I was trying to achieve the following steps:

1. parse the string into words by words list (array of strings). From upstream function I will get values of variables word_count, *line and remain.
2. concatenate them with a space at the end.
3. add space distributively, with left to right priority, so when a fair division cannot be done, the second to last word's end will have (no. of spaces) spaces, the previous ones will get (spaces + 1) spaces.
4. concatenate everything together to make it a new *line.

Here is a part of my faulty code:

int add_space(char *line, int remain, int word_count)
{
    if (remain == 0.0)
        return 0; // Don't need to operate.

    int ret;
    char arr[word_count][line_width];
    memset(arr, 0, word_count * line_width * sizeof(char));

    char *blank = calloc(line_width, sizeof(char));
    if (blank == NULL)
    {
        fprintf(stderr, "calloc for arr error!\n");
        return -1;
    }

    for (int i = 0; i < word_count; i++)
    {
        ret = sscanf(line, "%s", arr[i]); // gdb shows somehow it won't read in.
        if (ret != 1)
        {
            fprintf(stderr, "Error occured!\n");
            return -1;
        }
        arr[i] = strcat(arr[i], " "); // won't compile.
    }

    size_t spaces = remain / (word_count * 1.0);
    memset(blank, ' ', spaces + 1);
    for (int i = 0; i < word_count - 1; i++)
    {
        arr[0] = strcat(arr[i], blank); // won't compile.
    }

    memset(blank, ' ', spaces);
    arr[word_count-1] = strcat(arr[word_count-1], blank);

    for (int i = 1; i < word_count; i++)
    {
        arr[0] = strcat(arr[0], arr[i]);
    }

    free(blank);
    return 0;
}

It is not working, could you help me find the parts that do not work and fix them please? Thank you guys.