/in/foo.c: In function 'main':
/in/foo.c:8:14: warning: comparison between pointer and integer
    8 |         if(op=="+"){
      |              ^~
/in/foo.c:8:14: warning: comparison with string literal results in unspecified behavior [-Waddress]
/in/foo.c:10:20: warning: comparison between pointer and integer
   10 |         }else if(op=="-"){
      |                    ^~
/in/foo.c:10:20: warning: comparison with string literal results in unspecified behavior [-Waddress]
/in/foo.c:13:5: error: 'cout' undeclared (first use in this function)
   13 |     cout<<"%d\n",R<<endl;
      |     ^~~~
/in/foo.c:13:5: note: each undeclared identifier is reported only once for each function it appears in
/in/foo.c:13:21: error: 'endl' undeclared (first use in this function)
   13 |     cout<<"%d\n",R<<endl;
      |                     ^~~~
/in/foo.c:13:17: warning: left-hand operand of comma expression has no effect [-Wunused-value]
   13 |     cout<<"%d\n",R<<endl;
      |                 ^