Compilare: user.cpp:12:40: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] const levelType empty = { 0 , 0 , NULL }; ^ user.cpp: In function ‘void addOperator(char)’: user.cpp:127:13: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] overLap = NULL; ^ user.cpp: In function ‘void addBracket(char)’: user.cpp:135:13: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] overLap = NULL; ^ user.cpp: In function ‘int priority(char)’: user.cpp:32:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.cpp: In function ‘int execute(int, char, int)’: user.cpp:42:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.cpp: In function ‘int getNumber(char)’: user.cpp:89:27: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf ( f , "%c" , &c ); ^ user.cpp: In function ‘void read()’: user.cpp:162:37: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf ( f , "%c" , &c ); ^