Compilare: user.cpp: In function ‘bool calculate()’: user.cpp:134:40: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for(int i = 2; i < output.size(); i ++) ^ user.cpp: In function ‘int main()’: user.cpp:170:23: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(c,nmax+3,in); ^ user.cpp:174:25: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(in,"%d\n",&t); ^ user.cpp:175:24: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] fgets(k,nrmax+3,in); ^