Compilare: user.cpp: In function ‘int main()’: user.cpp:27:41: warning: comparison between signed and unsigned integer expressions [-Wsign-compare] for ( int j = 0; j < strlen(s[i]); ++j ) ^ user.cpp:47:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:123:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:158:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^ user.cpp:190:91: warning: NULL used in arithmetic [-Wpointer-arith] if ( s[i][q] == '+' || s[i][q] == '-' || s[i][q] == '=' || s[i][q] == NULL) ^