Main.cc: In function ‘int main()’:
Main.cc:7:22: error: storage size of ‘a’ isn’t known
int N,dem=0;char a[];scanf("%d",&N);
^
Main.cc:7:31: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
int N,dem=0;char a[];scanf("%d",&N);
~~~~~^~~~~~~~~