Which of the following function sets first n characters of a string to a given c

Which of the following function sets first n characters of a string to a given character?

2) What is the output of this C code?

#include <stdio.h>
     #include <string.h>
     int main()
     {
         char *str = "hello, world";
         char str1[9];
         strncpy(str1, str, 9);
         printf("%s %d", str1, strlen(str1));
     }

3) The library function used to find the last occurrence of a character in a string is

4) How will you print \n on the screen?

5) What will be the output of the program ?

 #include<stdio.h>
 int main()
 {
     int i;
     char a[] = "\0";
     if(printf("%s", a))
         printf("empty string\n");
     else
         printf("not empty string \n");
     return 0;
 }