I always find it so hard to help out proof-reading code for causes like this. Often, the code is more complicated than I find reasonable, while omitting things that make a lot of sense in "real" code, and it's very hard to know as an outside reader what the exact motivation for each decision was, by the author. A few such things that caused me to WTF: The initial few examples use a pointlessly static and global line…
I would agree, like all code this author definitely has a few quirks about how they write their C code, and I think all of your criticisms are valid. Their readline implementation is definitely sloppy, but they also just throw it in there without really talking about it. Adding to the readline issue, they definitely should have const'd the strings for readline and add_history. It's not just good practice, in this case it'd be required to conform to how readline's declaration is. I'm surprised they don't get warnings about passing a const char * into a char . Also, talking about the strcpy() and strlen(), the catch there is that it's actually removing the '\n' from fgets, it's not actually trying to terminate the string. That said, they should have just saved the strlen(buffer) result in a size_t and then used it later. The real function should look something like this:
/* Fake readline function */
char* readline(const char* prompt) {
fputs(prompt, stdout);
fgets(buffer, sizeof buffer, stdin);
size_t bufsiz = strlen(buffer);
char* cpy = malloc(bufsiz + 1);
strcpy(cpy, buffer);
cpy[bufsiz - 1] = '\0';
return cpy;
}