When does a char* ends with null in c?

I have confusion on char* null-termination so i have decided to make a study of cases i can find. Do these string literals end with a null?

1. char str1[512]="This is a random string"
2. char *str2 = strtok(buffer,"\n,") I have found its answer. This ends with null.
3. fgets(stdin, str3, 512)
4. scanf("%s",str4)
5. The code snippet:

   char str[5];    
   for(int i=0; i<5; i++) scanf("%c",&str[i]);
   

Note 1: I have an assumption that all standard functions in c library that returns a char*, null terminates the string.
Note 2: How do I check if a string is null terminated or not? (I tried this approach but it prints random stuffs imo.)

Edit: Just showing me a way to determine whether a string literal is null-terminated will be enough. I will go through each case and update here for future readers.

Such an example is by no means exhaustive, but it brings some clarity. The answer is actually simple. Any array of characters ending in '\0' is called a string. The programmer independently decides what he needs .

#include<stdio.h>

int main(void)
{
    char w[]="mamamia";
    int i;
    for(i=0;i<sizeof(w);i++)
    {
        if(w[i]=='\0')
            printf("w[%d]==null\n",i);
        else
            printf("w[%d]== %c \n",i,w[i]);
    }
    return 0;
}