Compiler output
prog.cpp:17:0: warning: "ONLINE_JUDGE" redefined [enabled by default]
<command-line>:0:0: note: this is the location of the previous definition
prog.cpp: In function ‘void back(int)’:
prog.cpp:24:24: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
prog.cpp:25:34: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
prog.cpp:30:47: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
