Structures help

Ok, i tried learning structures but i keep getting this error:
syntax error before '.' token

this is my code:

Code:

---

#include <iostream>

using namespace std;

        struct company {
                char name[50];
                int sales;
                int price;
                char owner[50];
        };

int main()
{
        cout<<"Enter the company name: \n";
        cin>>company.name; //get error here
        cin.ignore();
        cout<<"How many sales did it make? \n";
        cin>>company.sales; //and here
        cin.ignore();
        cout<<"How much did they sell it for? \n";
        cin>>company.price; //not to mention here
        cin.ignore();
        cout<<"Who is the company owner? \n";
        cin>>company.owner; //oh yea, and here too...
        cin.ignore();

        cout<<"Company: " << company.name << endl; //and here
        cout<<"Sales: " << company.sales << endl; //and here
        cout<<"Price: " << company.price << endl; //and here
        cout<<"Owner: " << company.owner << endl; //and here
}

---

anyone know what the problem is?

You need to create an object out of the struct.

i.e.

Code:

---

company companyObject;
        cout<<"Enter the company name: \n";
        cin>>companyObject.name;

---

Otherwise you don't have any space allocated for the data, the struct definition just tells the compiler of a new type of data holder that you have made. but you need to give it some memory first ;)

hmm... now im getting the same error but just on one line:

Code:

---

company company.name;

---

...

I suggest something closer to what Charmy posted, try to stay away from creating an instance of an object with the same name as the object... its just confusing.

Code:

---

company acompany;      // acompany is an instance of company
acompany.sales = 1200;  // Example setting 'sales' element

---

Ok, i tried doing what you said, but its still giving me that same error lol... structures are hard...

Your trying to access a member before its defined.

Code:

---

company company.name;

---

this won't work since your trying to access the name variable before the structure is even allocated. i needs to be like this

Code:

---

company companyO;
companyO.name = "Bobs Fish Shop";
companyO.sales = "2000.52";
//etc....

---

So you define the object. then once its defined, goto a new line and do the operations on all the variables.

Think of 'company' as a template. You have to create something from the template (namely, an object with the given data fields / available operations).

Code:

---

struct foo {
  int a;
  char b;
}; // 'foo' is now a template for a type of object, but no memory has been allocated yet

int main( ) {
  foo bar; // now memory has been allocated for an object variable 'bar' based off the template 'foo'
  bar.a = 5;
  bar.b = 'f';

  cout << bar.a << bar.b << endl;
/// etc...
}

---

Ok i dont quite get what your saying, but in ^^ that ^^ example you are defining the variables yourself, but i want then to be defined by when the user inputs something... im not quite sure if its the same and im just not thinking right... and why did you put

Code:

---

company company0;

---

??? what does that do exactly?

Based on your above code, are you writing company acompany.name?
Once you instantiate it: company acompany;
you only need the instantiated object name (acompany) before the '.' operator.

Code:

---

company acompany;
acompany.name = "a name";
acompany.sales = 10;
/* Not:
    company acompany;
    company acompany.name = "a name"; // error: company acompany is initialization
*/

---

Also, when you initialize it, you only put the type name, you can't set a variable in the struct and initialize it in the same statement.

Ok, i got it to work, but sadly still dont understand it 1 bit... why did i have to add:

Code:

---

company acompany;

---

?? couldnt i have just used company? and what exactly does that do anyways? is it making some kind of pointer from company to acompany? im so confused...

Quote:

---

Originally Posted by Goosie

Ok i dont quite get what your saying, but in ^^ that ^^ example you are defining the variables yourself, but i want then to be defined by when the user inputs something... im not quite sure if its the same and im just not thinking right... and why did you put

Code:

---

company company0;

---

??? what does that do exactly?

---

In my example, the following would have worked as well:

Code:

---

cin >> bar.a >> bar.b;

---

I just left that bit out for simplicity.

At any rate, read over my post again. Defining the structure 'company' does not allocate memory. It just makes a template. 'company company0' allocates memory for a variable named 'company0' based on the template, 'company'.

BTW here is the final code that i got:

Code:

---

#include <iostream>

using namespace std;

struct company {
        char name[50];
        int sales;
        int price;
        char owner[50];
};

int main()
{
        company acompany;

        cout<<"Enter the company name: ";
        cin>>acompany.name;
        cin.ignore();
        cout<<"How many sales did it make? ";
        cin>>acompany.sales;
        cin.ignore();
        cout<<"How much did they sell it for? ";
        cin>>acompany.price;
        cin.ignore();
        cout<<"Who is the company owner? ";
        cin>>acompany.owner;
        cin.ignore();

        cout<<"Company: " << acompany.name << endl;
        cout<<"Sales: " << acompany.sales << endl;
        cout<<"Price: " << acompany.price << endl;
        cout<<"Owner: " << acompany.owner << endl;
}

---

OOOHHHH... so typing:

Code:

---

company acompany;

---

is actualy giving the variables in "company" memory so it can actualy be used... and i make it acompany so that i dont get it confused with company? or so i can use the same "template" for diffrent things i would want to use it for? i think im starting to get it...

Sort of. You are on the right track. I briefly looked over your code, and it looks good.

A high level way of think about this (i.e. without thinking of memory layouts) is that 'company' is simply a type, like int, char, etc. So, the statements 'int x' and 'company acompany' are analogous: you create a named variable (x / acompany) of a given type (int / company). So, just like you would never say 'int = 3', you wouldn't say 'company.name = "something corp." '.

^ok that is making sense... i started writing a new code (i keep using what i learn to try and make it easier) and i'm getting some error saying incompatable types in assignment of 'const char[7] to char[50]' ...c++ is hard lol

OMG can someone please help me in why im getting that error?! lol

Code:

---

#include <iostream>

using namespace std;

struct people {
        char name[50];
        int age;
        char city[50];
};

int main()
{
        people person1;
        people person2;
        people person3;

        person1.name = "person1";
        person1.age = 18;
        person1.city = "city1";

        person2.name = "person2";
        person2.age = 19;
        person2.city = "city2";

        person3.name = "person3";
        person3.age = 20;
        person3.city = "city3";


        cout<<person1.name<<" is "<<person1.age<<" years old, and lives in "<<person1.city<<endl;
        cout<<person2.name<< " is " <<person2.age<<" years old, and lives in "<<person2.city<<endl;
        cout<<person3.name<<" is "<<person3.age<<" years old, and lives in "<<person3.city<<endl;
}

---

ok i fixed it, but it raises another question... i think i have the structures (to a decent level at least...)

Code:

---

#include <iostream>

using namespace std;

struct people {
        string name;
        int age;
        string city;
};

int main()
{
        people person1;
        people person2;
        people person3;

        person1.name = "person1";
        person1.age = 18;
        person1.city = "place1";

        person2.name = "person2";
        person2.age = 16;
        person2.city = "place2";

        person3.name = "person3";
        person3.age = 9;
        person3.city = "place3";


        cout<<person1.name<<" is "<<person1.age<<" years old, and lives in "<<person1.city<<endl;
        cout<<person2.name<< " is " <<person2.age<<" years old, and lives in "<<person2.city<<endl;
        cout<<person3.name<<" is "<<person3.age<<" years old, and lives in "<<person3.city<<endl;
}

---

but what is the diffrence between

Code:

---

char (name)[50];

---

and:

Code:

---

string (name);

---

?? can i just use string instead of char? since it seems string can support spaces, and char just gives errors...

Quote:

---

Originally Posted by Goosie

but what is the diffrence between

Code:

---

char (name)[50];

---

and:

Code:

---

string (name);

---

?? can i just use string instead of char? since it seems string can support spaces, and char just gives errors...

---

The difference is char (name)[50] is what you had to use in C programming, as well as a lot of other methods like strcpy and stuff to be able to get a text string correctly.. and in C++ its all done for you using a string.

char (name)[50] allocates 50 spaces for characters (which you have to copy using some str thing), but a string done it all for you, its the easist thing since slicing bread :p

And of course this tutorial is the ownage: http://www.cprogramming.com/tutorial/string.html

so i dont even need the char (name) [size] in c++? because every time i try to use it i get that same error message and it drives me crazy... :D thats beutiful to know! lol...

edit:

Oh yea... thanks everyone for helping me out :D i understand structures... entering day 4 of c++ and i can write programs that do absolutely nothing useful!!! lol... i was thinking of starting a text based game, but i dont know how to handle character names yet or functions... i'm hoping to be able to start on it within the next week or so :D

edit again:

Im tired and about to leave (just incase someone responds to this, i wount be here until the morning or later)

some clarification

string is a standard c++ library class which internally manipulates a array of chars, just like the one you declared "char name[]".
using directly an char array brings lots of constraints. And to manipulate it you have to use functions that iterate through out the array and apply the needed changes.
string is a class that internally does all that for you, and provides a simpler interface, so that you can manipulate it like any primitive variable.

About the struct - here's a clear explanation

Whenever you want to use a int what do you do ? what is a int ?

Code:

---

int y = 0;
y = y+2;
...

---

in that declaration you mention that y will be some variable that you'll manipulate. That variable is stored somewhere in memory. It doesn't mind.
int is the type of that variable. You're telling that y will be a integer. I could be a char, a float, some other type. You just have to choose.

Code:

---

struct company{
 ... //contents - don't really matter
};

---

in that declaration you're stating that company is the name of a structure. company will then be associated with a type of structures which was defined together with de declaration of struct company{}... In other words company will be a user defined type, as a short hand to the contents of the struct.
Then, like the instantiatoin of int y. you'll want to create an instance of that structure to manipulate it.

Code:

---

struct company x;
int            y;

---

now you're saying that x will be a variable to manipulate, just like y. The type of x is that of your defined structure, just like the type of y is a int.
so now you have an instance of your struct
you can create multiple instances of the same struct, each being independant one from another

Code:

---

struct company x, y;
struct company w;

---

now you want to fill the struct with something

Code:

---

struct company{
    char name[50];
    int sales;
};

struct company x;

---

if x is a instance of the structure, you will have instances of the structure variables within it. to acess each of the variables use the '.' operator

Code:

---

struct company x;
strcpy(x.name, "big deal" );
s.sales = 50;

---

when acessing a variable with the '.' operator just treat it normally as you would treat any variable of that type, like not being inside a struct

to end, you may want to create a instance of a struct with already defined values for each contained variable, or in other words, initialization values for each variable.
considering your struct

Code:

---

struct company {
    char name[50];
    int sales;
    int price;
    char owner[50];
};

struct company x = {
    "big deal" , //field name, which is char[]
    1000, //field sales which is a int
    50000, //field price which is a int
    "mister lazy" //field owner which is char[]
};

---

after that declaration, each of the structs contained variables will have those assigned values. And note that the order of the arguments for the initialization, is the same of the declaration of the struct



a structure simply holds a defined amount of variables to the programmers liking.

Quote:

---

#include<xErath.h>

---

You're out of date xErath, and in the near future your deprecated version may be removed from the standard or compilers, GL. :p

it's ansi C... deprecate yourself ;)

sorry, but im not getting the char and string variables still... every time i want to use char (with a structure at leat) i end up with an error, but string works perfectly...

What's your current code?

Quote:

---

Originally Posted by xErath

it's ansi C... deprecate yourself ;)

---

Oh.. I'm sorry what forum are you posting in again? ;) :p

currently im just making random programs to learn this stuff... i just started on a game that i plan on turning into a MUD codebase someday soon... right now im trying to get it to take a name, password, and race into a txt file... maybe im jumping a little ahead of myself, but im using it so i actualy have a set code that im working on instead of just random codes here and there...

playing around with char[] implies knowledge of c-style string manipulation which you'll learn. meanwhile std::string eases up things. yet you'll have to learn c-style strig manipulation, or you'll miss an important part of c/c++ programming.
a char[] is an array, therefore you can simply use it as you'd use a int or a float. but std::string overloads those operators.

Quote:

---

Originally Posted by xErath

playing around with char[] implies knowledge of c-style string manipulation which you'll learn. meanwhile std::string eases up things. yet you'll have to learn c-style strig manipulation, or you'll miss an important part of c/c++ programming.
a char[] is an array, therefore you can simply use it as you'd use a int or a float. but std::string overloads those operators.

---

I agree with xErath. I plan on going back to a C tutorial or two to practice char strings. I wouldnt use the char[] strings in my programs but I think learning it gives good base, especially for arrays. Plus one day you'll run across them and you'll want to know what does what so you can help convert it to C++ if thats the objective. Also alternatively I'm convinced char arrays may be the only way I'm going to get that text-data working with bitfield compression (std::string aint havin' :-/).. so thats an example, they may come in use where std::string doesnt.

Of course stick with std::string until checking out char[] strings feels comfortable, since std::string is a hell of a lot more convenient and easy.

Quote:

---

Of course stick with std::string until checking out char[] strings feels comfortable, since std::string is a hell of a lot more convenient and easy.

---

Convenient if you know all the internal function calls, and easier only if you need the features it comes with.

Any formal Programming training you get on C/C++ almost never introduces std::string until you are exteremly well versed in arrays, besides there are alot of instances when when using char arrays or char pointers is much more convenient than using std::string.

I would Suggest just playing around with arrays first you will quickly find their limitations, and how they work. I would actually advise that you don't use std::string until you understand the basics of how strings are stored in memory (i.e. the String is stored in the array with the null term char '\0' indicating its actually a string), and how to access each element of the string seperatly, becuase you use this same method to access them in the std::string class.

Trust me, you will be better off.

I can see that logic. I did read some C before skipping to C++ and I covered the concept of char arrays so maybe that made it easier. I just found, especially reading the basic std::string tutorial on this site (covering some of the function calls), that strings were much easier to use for basic console output (like his MUD game thing), but I didnt mean go any further than that without learning char strings.

And its not like you wouldnt have to learn function calls when learning char strings ;) but they tell you to learn it really early because thats a C tutorial where its necessary to know them to make strings, but in C++ it isnt so why not give it some time is all I meant.