C++ program doesn't print out strings but does output double value - c++

Question

So here is the program I'm working on. So far it just prints out the double value in my CPP file. Note the two characters arrays I have set up. Why is this?
Molecule.h
const int MAX_STRUCT = 10;
const int MAX_NAME = 20;
class Molecule {
char molecule_structure[];
char molecule_name[];
double molecule_mass;
public:
Molecule();
bool read();
void display() const;
};
Molecule.cpp
#include <iostream>
#include <cstring>
using namespace std;
#include "Molecule.h"
Molecule::Molecule() {
molecule_structure[0] = '\0';
molecule_name[0] = '\0';
molecule_mass = 0;
}
bool Molecule::read(){
bool complete = false;
cout << "Enter structure : ";
cin.getline (molecule_structure, 10);
if (strcmp (molecule_structure, "0") != 0){
cout << "Enter full name : ";
cin.getline (molecule_name, 20);
cout << "Enter weight : ";
cin >> molecule_mass;
cin.ignore();
complete = true;
}
else {
molecule_structure[0] = '\0';
molecule_name[0] = '\0';
molecule_mass = 0;
}
return complete;
}
void Molecule::display() const
{
cout << molecule_structure << " " << molecule_name << " " << molecule_mass << endl;
}
w4x.h
const int MAX_MOLECULES = 10;
w4x.cpp
#include <iostream>
using namespace std;
#include "w4x.h"
#include "Molecule.h"
int main() {
int n = MAX_MOLECULES;
Molecule molecule[MAX_MOLECULES];
cout << "Molecular Information\n";
cout << "=====================" << endl;
for (int i = 0; i < MAX_MOLECULES; i++) {
if (!molecule[i].read()) {
n = i;
i = MAX_MOLECULES;
}
cout << endl;
}
cout << "Structure Name Mass\n";
cout << "==================================================" << endl;
for (int i = 0; i < n; i++)
molecule[i].display();
}
The errors I believe are coming from my Molecule.cpp file which is what I've been changing around.
This is the output I'm currently receiving.
Molecular Information
=====================
Enter structure : Super
Enter full name : Man
Enter weight : 57
Enter structure : 0
Structure Name Mass
==================================================
57

Answer 1

Changing the header Molecule.h so it uses:
const int MAX_STRUCT = 10;
const int MAX_NAME = 20;
class Molecule {
char molecule_structure[MAX_STRUCT];
char molecule_name[MAX_NAME];
double molecule_mass;
public:
Molecule();
bool read();
void display() const;
};
Makes the code work sanely.
A more thorough reworking of the code to use std::string gives:
Molecule.h
#ifndef MOLECULE_H_INCLUDED
#define MOLECULE_H_INCLUDED
#include <string>
class Molecule
{
std::string molecule_structure;
std::string molecule_name;
double molecule_mass;
public:
Molecule();
bool read();
void display() const;
};
#endif // MOLECULE_H_INCLUDED
Molecule.cpp
#include <iostream>
#include <iomanip>
#include <limits>
#include <cstring>
using namespace std;
#include "Molecule.h"
Molecule::Molecule() : molecule_structure(""), molecule_name(""), molecule_mass(0) { }
bool Molecule::read()
{
Molecule m;
cout << "Enter structure : ";
if (!getline(cin, m.molecule_structure) || m.molecule_structure == "")
return false;
cout << "Enter full name : ";
if (!getline(cin, m.molecule_name))
return false;
cout << "Enter weight : ";
if (!(cin >> m.molecule_mass))
return false;
cin.ignore(numeric_limits<streamsize>::max(), '\n');
swap(*this, m);
return true;
}
void Molecule::display() const
{
cout << left << setw(15) << molecule_structure << " ";
cout << left << setw(20) << molecule_name << " ";
cout << setprecision(5) << molecule_mass << endl;
}
The read() function does not modify the variable it is given unless the reading is successful. There are probably better ways to handle the input, but that shown is reasonably sensible. You terminate the input with an empty line in response to the 'Enter structure:' prompt. The printf() format notations have the merit of brevity compared with what's necessary with C++ I/O streams.
w4x.cpp
No longer including w4x.h.
#include <iostream>
using namespace std;
#include "Molecule.h"
const int MAX_MOLECULES = 10;
int main()
{
int n = MAX_MOLECULES;
Molecule molecule[MAX_MOLECULES];
cout << "Molecular Information\n";
cout << "=====================" << endl;
for (int i = 0; i < MAX_MOLECULES; i++) {
if (!molecule[i].read()) {
n = i;
break;
}
cout << endl;
}
if (n > 0)
{
cout << "Structure Name Mass\n";
cout << "===================================================" << endl;
for (int i = 0; i < n; i++)
molecule[i].display();
}
}