how to check if char array was not changed after memset

how check if char array was not changed after using memset(char array, '\0', 1); or memset(char array, 0, 1);

using char array[0] == NULL, ==0, == '\0' and char array == NULL, == 0, =='\0' didnt work

btw printing array[0] giving me 0.

Any idea?

You're doing something wrong.
Perhaps using multiple local variables of type char and name array (based on your snippet)

Please post a small piece of complete example code which compiles, runs and documents the issue.

char messageFromPC2[80] = { 0 };
void setup() {
  Serial.begin( 9600 );
strcpy(messageFromPC2, "some string");
}
void loop() {
if (messageFromPC2[0] != 0) {
Serial.println("in")
}
memset(messageFromPC2, '\0', 1);

}

what is expected is first it doesnt get in conditional and second does but it does every single time

as mentioned above i tried conditions above too

what is expected is first it doesn't get in conditional and second does but it does every single time

I'm not clear about what you are saying.

When I run the code supplied I see the word "in" printed once. This is what I would expect if the messageFromPC2 first contained "some string" and then after the memset contained "'\0'ome string"

for me the second, third time still get in

agid:
for me the second, third time still get in

Then that's not the sketch you are running. Post your actual sketch.

agid:
I tried to post full code but it says too long here is the main part:

The accepted solution for that here, is to post your entire sketch as an attachment.

I have uploaded it Here. Also i have been few days trying to make this sketch smooth enough to be able to communicate throough bt with it but its buggy and for me i have short time to finish it before deadline :S. i would appreciatee every help even with ideas. Thanks

I have uploaded it Here.

You were asked to attach it. See section 8 in How to Use this Forum for details on how to make an attachment.

aarg:
The accepted solution for that here, is to post your entire sketch as an attachment.

Failing that, an MRE.