foo.cpp: In function 'int put(int)':
foo.cpp:53:12: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(i=0;i<strlen(s);i++)
           ~^~~~~~~~~~
foo.cpp:69:1: warning: no return statement in function returning non-void [-Wreturn-type]
 }
 ^
foo.cpp: In function 'int change()':
foo.cpp:49:1: warning: control reaches end of non-void function [-Wreturn-type]
 }
 ^