Compilare: user.cpp:13:50: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] const levelType empty = { maxInt , maxInt , NULL }; ^ user.cpp: In function ‘void solveTopLayers(char, int)’: user.cpp:77:33: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] equation . top() . operation = NULL; ^ user.cpp: In function ‘void addLeftArg(char)’: user.cpp:128:77: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] equation . top() . argL = (-1) * num , equation . top() . operation = NULL; ^ user.cpp: In function ‘void addOperator(char)’: user.cpp:139:13: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] overLap = NULL; ^ user.cpp: In function ‘void addBracket(char)’: user.cpp:147:13: warning: converting to non-pointer type ‘char’ from NULL [-Wconversion-null] overLap = NULL; ^ user.cpp: In function ‘int priority(char)’: user.cpp:33:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.cpp: In function ‘int execute(int, char, int)’: user.cpp:43:1: warning: control reaches end of non-void function [-Wreturn-type] } ^ user.cpp: In function ‘int getNumber(char)’: user.cpp:115:33: 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:174:37: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf ( f , "%c" , &c ); ^