C++ Vectors (of Vectors!) Woo hoo! 2-dimensional matrices!

Why we need them:

2-d vectors allow us to analyze data, keep track of 2-d data sets, and program basic games.

A vector is declared using the following format:
vector<type> name; // for size zero
vector<type> name(size); //for a vector of integer 'size'

A 2-d vector is declared like this:
vector<vector<int> > table(sizeV, sizeV);

Other useful vector commands:
vectorName.pop_back(); // removes the last element of the vector
vectorName.size(); // returns the number of elements of the vector
vectorName.push_back(variable); // adds variable to the end of the vector, i.e. makes the variable bigger!
vectorname.resize(newsize); // changes the vector to be of size newsize
vectorname.resize(newsize, element); // changes the vector to be of size newsize, and fills the new spots with element

Example program that a 2-d vector, and fills it with zeros and ones:

// example program using vectors of vectors
// this program creates a vectors of vectors (a table)
// and then fills the table with ones or zeros,
// based on a user specified probability

#include <iostream>
#include <vector>

using namespace std;

int main ()
{
    	cout << endl;
    	cout << "This program creates a vector of vectors (called a table) " << endl;
   	cout << "and fills each element with either a zero or one, based on" << endl;
   	cout << "a user-specified probability." << endl << endl;
   	cout << "Please input size of list to be input: ";

    	int sizeV;

    	cin >> sizeV;

   	cout << endl;
    
   	// now declare vector of appropriate size

    	vector<vector<int> > table(sizeV, sizeV);

    	// ask for probability of having a one in each element

    	cout << "Please input the probability of having a one in ";
	cout << "each element: ";
    
	double probONE;
	
	cin >> probONE;
	
	cout << endl;

	// error checking to weed out those too ignorant to know what a probability is
	// using a loop that will continue until the user gets it right!
	

	while (	(probONE < 0) or (probONE > 1) )
		{	cout << "The probability of something must be between zero and one. Please try again.";
			cout << endl << endl;

			cout << "Please input the probability of having a one in";
			cout << "each element: ";
    
			cin >> probONE;
		}

	// now fill the table with ones and zeros
	// I will use nested whiles because we haven't gotten to "for" loops yet
	
	int i = 0;
	int j = 0;
	
	while (i < sizeV)
		{
			j = 0;
			while (j < sizeV)
				{
					if (probONE > static_cast<double>(rand())/RAND_MAX )
						{table [i] [j] = 1;}
					else
						{table [i] [j] = 0;}
					j=j+1;
				}
			i=i+1;
		}	
	
	// need to output the table to the screen

	i = 0; // remember not to redeclare these counters, just zero them out again
	j = 0;
	
	while (i < sizeV)
		{
			j = 0;
			while (j < sizeV)
				{
					cout << table [i] [j] << " ";
					j=j+1;
				}
			cout << endl;
			i=i+1;
		}	
		
	cout << endl; // add one more carriage return to make the screen look pretty

	return 0;
	}