Strange strncpy response

Question

I just run this code and what i get for n=1 is not what i expect to get. Can you explain why is this happening?

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXRIGA 11
int main()
{
    char s[MAXRIGA+2];
    char a[MAXRIGA]="pippo";
    strncpy(s, a, 1); //       n=1
    printf("%s", s);
    return 0;
}

returns

pF

instead if n=2 or more i get what i want.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define MAXRIGA 11
int main()
{
    char s[MAXRIGA+2];
    char a[MAXRIGA]="pippo";
    strncpy(s, a, 2); //       n=2
    printf("%s", s);
    return 0;
}

returns

pi

Answer 1

From man strncpy:

The strncpy() function is similar, except that at most n bytes of src are copied. Warning: If there is no null byte among the first n bytes of src, the string placed in dest will not be null-terminated.

You are copying only one byte from the source string, which is not a null-terminator. So you get an undefined behavior here, as trying to print a non-terminated string. The same for n=2, which appears to work by accident.