Compilare: user.cpp: In function ‘int main()’: user.cpp:11: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:12: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result user.cpp:13: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result user.cpp: In function ‘int exp()’: user.cpp:43: warning: array subscript has type ‘char’ user.cpp:44: warning: array subscript has type ‘char’ user.cpp:49: warning: array subscript has type ‘char’ user.cpp:50: warning: array subscript has type ‘char’ user.cpp:58: warning: array subscript has type ‘char’ user.cpp:41: warning: suggest explicit braces to avoid ambiguous ‘else’ user.cpp:61: warning: array subscript has type ‘char’