/in/foo.cc: In function 'void scan()':
/in/foo.cc:89:14: warning: suggest parentheses around '&&' within '||' [-Wparentheses]
     if(x==-1 && y!=-1 || (y!=-1 && x!=-1 && x>y)){
        ~~~~~~^~~~~~~~
/in/foo.cc:136:3: warning: 'check_num' may be used uninitialized in this function [-Wmaybe-uninitialized]
   if(check_num== ans)
   ^~
/in/foo.cc:94:23: warning: 'y' may be used uninitialized in this function [-Wmaybe-uninitialized]
     if(x!=-1 && y!=-1 && x<y)
        ~~~~~~~~~~~~~~~^~~~~~
/in/foo.cc:94:23: warning: 'x' may be used uninitialized in this function [-Wmaybe-uninitialized]