/in/foo.cc:2:0: warning: ignoring #pragma GCC opmitize [-Wunknown-pragmas]
 #pragma GCC opmitize(2)
 
/in/foo.cc: In function 'double cal(double)':
/in/foo.cc:10:9: warning: unused variable 'i' [-Wunused-variable]
     int i, j;
         ^
/in/foo.cc:10:12: warning: unused variable 'j' [-Wunused-variable]
     int i, j;
            ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:18:12: warning: unused variable 'j' [-Wunused-variable]
     int i, j;
            ^