How to copy arrays of arrays in C? (array of string to another array of string)

I'm doing Zed Shaw's Learn C The Hard Way course. On exercise 11, in the extra-credit question #2, he askes:

1. Make these loops count backward by using i-- to start at argc and count down to 0. You may have to do some math to make the array indexes work right.

2. Use a while loop to copy the values from argv into states.

I try:

#include <stdio.h>

int main(int argc, const char *argv[]){

    int i = argc - 1;
    while(i >= 0){
        printf("arg %d: %s\n", i, argv[i]);
        i--;
    }

    char *states[] = {
        "California", "Oregon",
        "Washington", "Texas"
    };

    int num_states = 4;
    i = num_states - 1;
    while( i >= 0){
        printf( "state %d, %s\n", i, states[i]);
        i--;
    }

    i = 0;
    while(i < argc && i < num_states){
        int j = 0;
        while( (states[i][j++] = argv[i][j++]) != '\0' ){
            i++;
        }
        states[i][j] = '\0';
    }

    i = num_states - 1;
    while( i >= 0){
        printf( "state %d, %s\n", i, states[i]);
        i--;
    }

    return 0;
}

I get a Segmentation Fault. I understand that you can't copy arrays in C, that they are const pointer or something similar (or so I read). That's why I try to copy character by character:

while(i < argc && i < num_states){
    int j = 0;
    while( (states[i][j++] = argv[i][j++]) != '\0' ){
        i++;
    }
    states[i][j] = '\0';
}

Yet it doesn't work. How should I do this? The compiler gives me this warning when I compile:

$ make ex11
cc -Wall -g    ex11.c   -o ex11
ex11.c: In function ‘main’:
ex11.c:26:28: warning: operation on ‘j’ may be undefined [-Wsequence-point]

I don't get why it says that j is undefined. valgrind says this:

$ valgrind ./ex11 this is a test
==4539== Memcheck, a memory error detector
==4539== Copyright (C) 2002-2012, and GNU GPL'd, by Julian Seward et al.
==4539== Using Valgrind-3.8.0 and LibVEX; rerun with -h for copyright info
==4539== Command: ./ex12 this is a test
==4539== 
arg 4: test
arg 3: a
arg 2: is
arg 1: this
arg 0: ./ex11
state 3, Texas
state 2, Washington
state 1, Oregon
state 0, California
==4539== 
==4539== Process terminating with default action of signal 11 (SIGSEGV)
==4539==  Bad permissions for mapped region at address 0x400720
==4539==    at 0x4005F1: main (ex11.c:26)
==4539== 
==4539== HEAP SUMMARY:
==4539==     in use at exit: 0 bytes in 0 blocks
==4539==   total heap usage: 0 allocs, 0 frees, 0 bytes allocated
==4539== 
==4539== All heap blocks were freed -- no leaks are possible
==4539== 
==4539== For counts of detected and suppressed errors, rerun with: -v
==4539== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 2 from 2)
Segmentation fault

[EDIT 1] A switched my code for this

int i = 0;
while( i < argc && i < num_states ){
    states[i] = argv[i];
    i++;
}

It does work, but the compiler gives me a warning. Also, I realized after posting this question that my previous:

while( (states[i][j++] = argv[i][j++]) != '\0' ){
    i++;
}

Is just plain wrong. Because the j++ is executed twice per loop, and that i++ should be outside that loop in the outer loop. And also as mentioned in the comment below, that the byte-by-byte copy that I try to do using array of arrays doesn't work because I actually have array of pointers.

That said, is there a way I could do this without having the compiler's warning?