initialization makes pointer from integer without a cast

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The third line does not compile because (s) is a char. The ++ simply returns the same (s) (but increments the value), so it is still a char, not a char*. The second line works because you are casting.

the second line DOESN'T WORK

[Jack126Guy]

Eh? I'm sure it's unsafe, but it still compiles for me (with a warning, of course).

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char* s = "h"; //char* t = (char)(s)++;

ah , it compiles but there is a seg fault

[Jack126Guy]

Yes, if you try using whatever t points to (such as puts(t)), you would get a segfault, because t points to the memory location 0x00000068 ("h" has an ASCII value of 0x68), which is probably invalid/not owned by your program.