Compilare: user.cpp: In function ‘int main()’: user.cpp:32:91: warning: array subscript has type ‘char’ [-Wchar-subscripts] if( ( sf_L[i]-inc_L[i] + sf_C[j]-inc_C[j] + 2 ) & 1 ) a[i][j] = opus[ a[i][j] ]; ^ user.cpp:36:41: warning: array subscript has type ‘char’ [-Wchar-subscripts] a[i][j] = opus[ a[i][j] ]; ^ user.cpp:16:13: warning: unused variable ‘jj’ [-Wunused-variable] int i,j,jj,N,M,L,ans=0; ^ user.cpp:13:38: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("electrica.in","r",stdin); ^ user.cpp:14:40: warning: ignoring return value of ‘FILE* freopen(const char*, const char*, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] freopen("electrica.out","w",stdout); ^ user.cpp:19:33: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result] scanf("%d %d %d\n",&N,&M,&L); ^ user.cpp:20:61: warning: ignoring return value of ‘char* fgets(char*, int, FILE*)’, declared with attribute warn_unused_result [-Wunused-result] for(i = 1; i <= N; ++i) fgets( a[i] + 1, NMax-1, stdin ); ^