int main(int argc, char *argv[])
{
    // Check for arguments and file pointer omitted
    FILE *f = fopen(argv[1], "r");
    char *times;
    int i = 0;

    for (i = 0; i < 2000; i++)
    {
        char line[80];
        if (fgets(line, 80, f) == NULL)
            break;

        //I want every line with the text "</time> to be added to string times
        if(strstr(line, "</time>"))
        {
            times = strcat(times, line);  //This line is my problem
        }
    }

    printf(times);

    fclose(f);
    return 0;
}