Compilare: main.cpp: In function 'int main()': main.cpp:10:11: warning: converting to non-pointer type 'char' from NULL [-Wconversion-null] ch1 = NULL; ^~~~ main.cpp:6:37: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("text.in" , "r" , stdin); ^ main.cpp:7:39: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)', declared with attribute warn_unused_result [-Wunused-result] freopen("text.out" , "w" , stdout); ^