Thread: A few questions in C++

Originally Posted by ThWolf

Edit:
BTW, in the book I learned that in order to input a string, you need a char array. Never thought that you can do "string name", for example.

Ick. Just ick. You can do character arrays (which are the C-style way of doing things) but I'd never use an array when a std::string would do the job better. And it does the job better most of the time. Yes, you should learn how to use character arrays. And learn that most of the time there are better options

Arrays have a lot of pitfalls. Say you make a 20 character array for a person to enter their name. Joe User enters 30 characters. Best case scenario, he just crapped all over your stack. Worst case, he's able to execute arbitrary code by very carefully crafting his string.

If you're serious about learning C++, I strongly encourage you to pay special attention to learning about a few areas, once you've got the basics down:

* Classes. I know you don't know them now. Once you learn to use them you'll wonder how on earth you ever coded without them.

*Standard Template Library (STL). std::string is one of very many powerful tools that you'll find here. You'll find vectors (like arrays, but can grow or shrink in size), lists (optimized for insertion/deletion speed, but you can't easily skip around within them), maps (optimized for very fast insertion/deletion/access of very large amounts of data), and many others.

Sadly C++ lacks classes for vector/matrix arithmatic. std::vector is like an array except its size is not constant; you can increase or decrease it as the program runs.

For example:

Code:

#include <vector>
#incude <iostream>

int main(int, char**){
	// Make a vector which can store 5 ints, then fill it with 0 2 4 6 8
	std::vector<int> myVector(5);
	for (int i = 0; i < myVector.size(); i++){
		myVector[i] = 2*i;
	}

	// Print it
	std::cout << "Initial vector: " << std::endl;
	for (int i = 0; i < myVector.size(); i++){
		std::cout << "myVector[" << i << "] = " << myVector[i] << std::endl;
	}

	// This adds the number 10 to the end of the vector.  It increases the size of the vector
	// from 5 to 6 to accomplish this task.
	myVector.push_back(10);

	// Print it again
	std::cout << "Final vector: " << std::endl;
	for (int i = 0; i < myVector.size(); i++){
		std::cout << "myVector[" << i << "] = " << myVector[i] << std::endl;
	}
}

In that example, it starts out as an array of 5 integers, but the size grew automatically to 6 when I added a new element using push_back.

Oh, and I forgot to mention that is true about string as well -- it can grow or shrink to accomodate the data you put in it.

All STL (standard template library) containers are nice like this. They also keep track of their size, so when you pass them to other functions you don't need to pass a pointer and the length separately; the vector knows its own length and will tell you if you ask it nicely

As to the book: Haven't read it. But the author is good, and the 4th ed. is supposed to be a really good improvement over the priors. Should be a very good one to learn from.

Your book will definately teach you about C++ style std::string if you give it time They do need to teach you how to do things with char arrays, even if they're less useful later, as they still have their uses. There do come times when a char array is better than a string, so it's very important to know both and choose between them wisely. I think the book will do a good job on that.

>> As to the book: Haven't read it. But the author is good, and the 4th ed. is supposed to be a really good improvement over the priors. Should be a very good one to learn from.

I think you're thinking of C++ Primer by Lippman, Lajoie and Moo. ThWolf mentioned C++ Primer Plus, which is unrelated and doesn't have nearly as good of a reputation.

>> Your book will definately teach you about C++ style std::string if you give it time.
Switch to C++ Primer (without the Plus) or Accelerated C++.