what is almost correct (C Progamming )

Question

Hi,

My teacher told me that we do not need [80] in --->  while (c1[80]!=c2[80]) {

And she said it has to be [0]
I am not sure if we also need value of 0 in ---> char c1[80], c2[80];
It is regards to my assignment and important of not losing marks on some rubbish mistakes
___________________

#include <stdio.h>

#include <string.h>

char c1[80], c2[80];

int main() {

    printf("Please enter card type:\n");

    gets(c1);                                                                                                                                       

    gets(c2); 

    while (c1[80]!=c2[80]) {

       strcpy(c1,c2);

        gets(c2);

    }

        printf("SNAP");

}