why get 'ac'  used  ""pascl""

var n:int64;

begin

  readln(n);

  writeln(n*n);

  writeln(n);

end.
---------------------------------
but:
 #include<stdio.h>
int main()
{  unsigned  long long n;
               scanf("%lld",&n);
               printf("%lld\n",n*n);
               printf("%lld\n",n);
 return 0;
}

who could tell me when i use "c",get "wa"?   i am confused;

read FAQ
for long long you should use %I64d

thanks!