/in/foo.cc: In function 'int main()':
/in/foo.cc:17:34: error: expected primary-expression before '<=' token
  for(i=1;i<=n;i++)if(a[i]-a[i-1])<=k)
                                  ^~
/in/foo.cc:7:13: warning: unused variable 'flag' [-Wunused-variable]
     int n,k,flag=1,i;
             ^~~~