Compilare: main.cpp: In function 'void calcul_prefix(char*)': main.cpp:11:6: warning: unused variable 'a' [-Wunused-variable] int a[n][n]; ^ main.cpp: In function 'int main()': main.cpp:69:11: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(i=0;i<poz.size();i++) ~^~~~~~~~~~~