CS50 pset3 Music segmentation fault

Question

Today I finished the music project, or at least I think I've finished it. On helper.c when I run make it makes both notes and synthesizer files and with no errors. But when I want to run ./notes it gives me segmentation fault error. Even when I ran the program with check50 it gave me this error:

failed to execute program due to segmentation fault

I personally think it might be because of turning string to int or the way I got the notes from the string. First I introduced one string for taking the note and one int for taking the ovtav of the note.

The string note is something like D4 or C#4

So I will just copy this part, to check with you if I've done it correctly.

string noteletter="";
int noteoctav;
if (strlen(note) == 3)
{
    noteletter[0] = note[0];
    noteletter[1] = note[1];
    noteoctav = note[2] - '0';
}
if (strlen(note)== 2)
{
    noteletter[0] = note[0];
    noteoctav = note[1] - '0';
}

Update

Here I've added the full code so you can see what I am trying to do.

Answer 1

Two problems I can see (assuming string is a typedef of char* )

if noteletter has a length of 0 (value = "" ) then what do you think noteletter[1] is doing?

Even if noteletter was set to something bigger (eg noteletter = "ABC"; ) - writing to a literal string is undefined behavior.

Try char noteletter[3] = { 0 }; to get something that (at a quick glance) looks big enough.

Another possible issue: if note is NULL or invalid then strlen(note) is not safe.

Answer 2

(Posted answer on behalf of the question author)

My problem was that I defined noteletter as string. I changed that part to

char noteletter[4];
int noteoctav;
if (strlen(note) == 3)
{
    noteletter[0] = note[0];
    noteletter[1] = note[1];
    noteletter[2] = '\0';
    noteoctav = note[2] - '0';
}
if (strlen(note)== 2)
{
    noteletter[0] = note[0];
    noteletter[1] = '\0';
    noteoctav = note[1] - '0';
}

and now it works :)