Compilare: user.cpp: In function ‘void prec()’: user.cpp:46:39: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 4; i < powers.size(); i++) ^ user.cpp: In function ‘char nextch()’: user.cpp:15:34: warning: ignoring return value of ‘size_t fread(void*, size_t, size_t, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fread(buf, 1, MAXBUF, fi); ^