Compilare: user.cpp: In function ‘int main()’: user.cpp:34:10: warning: unused variable ‘dx’ [-Wunused-variable] int dx = 0; ^ user.cpp: In function ‘char* infix2prefix(FILE*)’: user.cpp:160:10: warning: unused variable ‘digits’ [-Wunused-variable] char digits[20]; ^ user.cpp:161:9: warning: unused variable ‘efx’ [-Wunused-variable] int efx = 0; ^ user.cpp:208:1: warning: no return statement in function returning non-void [-Wreturn-type] } ^ user.cpp: In function ‘int eval(tree_node*)’: user.cpp:71:1: warning: control reaches end of non-void function [-Wreturn-type] } ^