Why are there 2 extra characters always added to this string?

I am writing a program in C, where I generate multiple strings made up from random characters. Essentially the size of each string is fixed, set to be 8 characters, and a random character is inputted for every index of the string, accounting that the last index is the null terminating character.

However, whenever I go to print the strings, I get 2 extra characters added to them, and the strlen() function returns a length of 10 instead of 8.

This is how the output looks like:

And this is the code:

char password[9];
for(int cnt = 0; cnt < n; cnt++){
    for(int i = 0; i < 8; i++){
        if (i < 3){
            password[i] = rand() % 26 + 65;
        } else if (i < 6){
            password[i] = rand() % 26 + 97;
        } else if (i >= 6){
            password[i] = rand() % 10 + 48;
        }
    }
    printf("%s\n", password);
    printf("%d\n", strlen(password));

I tried to make a random string generator, I was expecting the string to be the same size that I set it to be.

>Solution :

char password[9]; declares an array that provides 9 characters worth of data, but it doesn’t initialize them to anything (unless it’s a static or global variable, that is); it’s got whatever garbage happened to be in the memory it occupies. You fill in 8 characters, and the 9th character is left uninitialized. When treated as a C-style string, if none of those characters are NULs, you read off the end of the array into adjacent memory, and keep going until it hits a NUL by coincidence (and decides it’s done), or reaches unreadable memory (and crashes).

To ensure it’s properly NUL terminated before treating it as a C-style string, either:

• Change the declaration to initialize the characters to zeroes:

  char password[9] = {0};

• or explicitly set a NUL terminator at some point:

  password[8] = '\0';