Thread: Problem with variable

Hi,

Im fairly new with programming. Im following up my last class on programming with c++.

The question i have is very simple.

Lets say you want to create 10 different variables and give them name hello1 hello2 etc...

I want to use for(). But the problem I have is that i can't understand how you can use a variable for defining a variables name.

example:

Code:

#include <iostream>
using namespace std;

int main (){

int i;


for(i = 0; i<10; i++){

char hello(i);*
cin >> hello(i);**
cin.ingore(1000, '\n');
}

//this would give us the input for our hello0 and hello5 variable.
cout << endl << endl << hello0 << hello5;

return 0;
}

*(this is where I want i to be, so that for() can create 10 different hello variables with the name hello0 hello1 hello2 etc...)

**(i.... same here, each time for() goes a lap i want the next variable to be used in the cin phrase)

You probably want to use an array. Read the tutorial on arrays.

I would not like to use an array. I just want to create 10 variables. by using a variable i for defining each variables name.

C++ does not have variable variables, so barring some unnecessary yet creative macro tricks (that I do not know of) this is not possible. Generally an array really is the correct solution when you are faced with such a problem.

strange it seems like such an easy thing to implement.

It is indeed an easy thing to implement... with arrays.

Originally Posted by AdampqmabA

strange it seems like such an easy thing to implement.

If you think that, you don't understand the separation of compilation and execution yet.

Originally Posted by AdampqmabA

strange it seems like such an easy thing to implement. Well then i will just read more about arrays then :/

It would be relatively easy to make dynamic variables in a language where variables are created at runtime (when the application runs). In C and C++, ALL variables are created at compile-time [there are ways around that, but that involves pointers (which is a sort of variable that holds a reference to a lump of memory that can in turn hold other things), which is a couple of steps away from where you are at the moment, I suspect], so the compiler needs to know what value i has to make the variable for you. Since that is impossible for the compiler to know in most situations (including this one, as i changes throughout the runtime of the application), it doesn't work like you expect.

The reason C and C++ are not createing variables at runtime has to do with the extra overhead that is involved with that. That is what makes C and C++ really fast to run. But it means some extra work at compile time and sometimes extra work for the programmer. You can't have it both ways, I'm afraid.

Laserlight, I don't think macros would work. Templates perhaps, but even that would probably be streatching it in this case.

--
Mats

Originally Posted by matsp

Laserlight, I don't think macros would work.

Neither do I, but my lack of knowledge of the more creative aspects of the preprocessor is enough for me to give it the benefit of the doubt.

Originally Posted by matsp

Templates perhaps, but even that would probably be streatching it in this case.

Templates won't cut it, or we can claim that arrays are variable variables.

Actually, macros would work. The code would be completely unreadable.