Compilare: user.cpp: In function ‘int main()’: user.cpp:28:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int j = 0; j < strlen(s[i]); ++j ) ^ user.cpp:48:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:71:69: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == NULL ) ^ user.cpp:96:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:129:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:164:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:196:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^