Need help iterating through a char ** pointer array

[solar axle]

I have a homework assignment where I have to create a function called add_string(char **existing, const char *add) which also returns a **char type. The goal is to basically make a new array that copies all of the existing array of strings and appends the add string on the end as well.

I am having some difficulty figuring out how to actually iterate through the **existing array that has been passed through.

I have tried inputing a for loop and looping that way. I tried just outputting existing, with printf("%c", *existing[0]); And my most recent attemp has been this:

char *ptr = *existing;
       
    while(ptr != NULL)
    {
        printf("test");
        fflush(stdout);
        ptr++;
    } 

Currently my output is this:
timeout: the monitored command dumped core

Could anybody help me figure out how to correctly iterate through this array of strings?

[dapper tundra]

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[ruby kelp]

that would depend on what exectly exsiting is, and how it was constructed. pointers don't hold any info about the length of the 'thing' they point to. i would assume existing hold it somewhere(?)

usually thats done by setting the last char * to NULL

if thats indeed the case - one can do:

for(; *exisitng; exisiting++) {
  puts(*exisiting);
}```

otherwise - you'd need to know how many 'strings' exsiting points to

[solar axle]

i've been told that they have NULL in the last location

[ruby kelp]

then

[solar axle]

so how would i print that value using printf so I can see what is stored in existing?

[ruby kelp]

in the exact same way, replacing puts with printf("%s\n", ...) i guess. what wrong with puts exactly?