c - printf outputting garbage instead of specific characters

Question

Well I've weird problem with printf(). It's outputting garbage on screen. It's kind of connected with memory I guess. Have a look:

char string1[] = "SAMPLE STRING";
char string2[20]; // some garbage in it

/* let's clear this madness*/
int i = 0;
for (i; i < 20; i++) string2[i] = ' ';   // Space, why not.

printf("output: %s", string2);

OUTPUT

output:      ╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠╠SAMPLE STRING
// ten spaces and random characters, why?

Answer 1

Because C strings need to be NUL terminated. This means the last char of your string must be ''. This is how printf (and all other C string functions) know when a string is finished.