Compilare: user.cpp: In function ‘int main()’: user.cpp:38:16: warning: array subscript has type ‘char’ [-Wchar-subscripts] fr[c[i]]++; ^ user.cpp:39:19: warning: array subscript has type ‘char’ [-Wchar-subscripts] if(fr[c[i]]==1)M++; ^ user.cpp:40:24: warning: array subscript has type ‘char’ [-Wchar-subscripts] else if(fr[c[i]]==2)K++; ^ user.cpp:35:30: warning: ignoring return value of ‘int fscanf(FILE*, const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] fscanf(f,"%d\n%s",&N,c+1);len=strlen(c+1);len-=(c[len]=='\n'); ^