/in/foo.cc: In function 'int calc(int, int)':
/in/foo.cc:30:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<strlen(s);i++){  
                 ~^~~~~~~~~~
/in/foo.cc: In function 'int check()':
/in/foo.cc:38:18: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
     for(int i=0;i<strlen(s);i++) {  
                 ~^~~~~~~~~~