How to pass an array to a class? - c++

Question

#include <iostream>
#include <string>
using namespace std;
class Term;
class Polynomial;
class Term {
public:
friend class Polynomial;
void set_term(string s);
int get_pow();
int get_coefficient();
private:
int coefficient;
int pow;
};
class Polynomial {
public:
friend class Term;
Polynomial(int s, Term t[]);
int get_size();
Term *myterm;
private:
int P_size;
};
void Term::set_term(string s) {
coefficient = stoi(s.substr(1, 1));
pow = stoi(s.substr(4, 1));
if (s[0] == '-') {
coefficient = -coefficient;
}
}
int Term::get_coefficient() { return coefficient; }
int Term::get_pow() { return pow; }
Polynomial::Polynomial(int s, Term t[]) {
P_size = s;
myterm = new Term[s];
for (int i = 0; i < s; i++) {
myterm[i].coefficient = t[i].coefficient;
cout << i << " Term " << t[i].coefficient << endl;
cout << i << " Polynomial " << myterm[i].coefficient << endl;
myterm[i].pow = t[i].pow;
}
}
Polynomial::get_size() { return P_size; }
int main() {
string x1;
cin >> x1;
int size_x1 = x1.size();
Term term1[size_x1];
for (int i = 0; i < size_x1; i += 5) {
term1[i].set_term(x1.substr(i, 5));
}
Polynomial p1(size_x1 / 5, term1);
for (int i = 0; i < size_x1; i += 5) {
cout << term1[i].get_coefficient() << "x^";
cout << term1[i].get_pow() << endl;
}
cout << "------------------" << endl;
for (int i = 0; i < p1.get_size(); i++) {
if (p1.myterm[i].get_coefficient() > 0)
cout << "+";
cout << p1.myterm[i].get_coefficient();
cout << "x^";
cout << p1.myterm[i].get_pow() << endl;
}
return 0;
}
term1 in main is working right but when I pass it to p1(Polynomial) just t[0] and, myterm[0]
is true I mean I pass term1 to p1 as t so t[0] = term1[0] and myterm[0] = t[0]
Polynomial::Polynomial(int s, Term t[]) {
P_size = s;
myterm = new Term[s];
for (int i = 0; i < s; i++) {
myterm[i].coefficient = t[i].coefficient;
cout << i << " Term " << t[i].coefficient << endl;
cout << i << " Polynomial " << myterm[i].coefficient << endl;
myterm[i].pow = t[i].pow;
}
}
in Polynomial constructor both t[1].coeffient and, myterm[1].coefficient are 4941660(for instance)
however, t is term1 and in term1 term1[1] is the 4(for instance)
if term1[1] is 4 so t[1] should be 4 but it's not so myterm[1], is not 4 too.

Answer 1

There's a lot of confusion over sizes here
string x1;
cin >> x1;
int size_x1 = x1.size();
Term term1[size_x1];
for (int i = 0; i < size_x1; i += 5) {
term1[i].set_term(x1.substr(i, 5));
}
Polynomial p1(size_x1 / 5, term1);
You didn't say what your input is, but suppose it is "1234567890" then size_x1 equals 10, so term1 will also have size 10. Then your for loop will execute twice, with i equal to 0 and i equal to 5, so you will assign 12345 to term1[0] and 67890 to term1[5]. That makes no sense to me. term1 has size 10 but the only elements assigned to are zero and five.
Then you create p1 with size size_x1/5 which equals 2. So the constructor for p1 will look at term1[0] and term1[1], but in the for loop you assigned to term1[0] and term1[5].
You have to think carefully about what the code you are writing is actually doing. The compiler will do exactly what you tell it to. It's not like talking to a person who can understand what you really meant. So you have to be very careful. This is I think you really meant (but I could be wrong)
string x1;
cin >> x1;
int size_x1 = x1.size();
int size_term1 = size_x1/5;
Term term1[size_term1];
for (int i = 0; i < size_term1 ; ++i) {
term1[i].set_term(x1.substr(5*i, 5));
}
Polynomial p1(size_term1, term1);
I created a new variable size_term1 with the size of the term array, which is now the sizeof the input divided by 5. And I changed the for loop so that it assigns to term1[0] and term1[1].
So your problem has nothing to do with passing an array to a class, which you did perfectly correctly. It was not thinking clearly about the code you were writing, and making mistakes in the logic.