Compilare: user.cpp: In function ‘int main()’: user.cpp:34:10: warning: unused variable ‘dx’ [-Wunused-variable] int dx = 0; ^ user.cpp: In function ‘void infix2prefix(FILE*)’: user.cpp:159:10: warning: unused variable ‘digits’ [-Wunused-variable] char digits[20]; ^ user.cpp:160:9: warning: unused variable ‘efx’ [-Wunused-variable] int efx = 0; ^ user.cpp: In function ‘int eval(tree_node*)’: user.cpp:70:1: warning: control reaches end of non-void function [-Wreturn-type] } ^