ending array entry?

[PinkR0ck]

I'm writing a program that asks the user to enter 3 sets of numbers (max # in each set is 20), and after all 3 sets are entered, the program would display them.
The issue i'm having is how to end the entries as the user can enter 20 OR less characters. And also, if the user enters more, the extra numbers are automatically being moved to the next array, rather than just being ignored (which is what I want to do).

#include <iostream>
using namespace std;

int a, b, c;	

int A[20];
int B[20];
int C[20];

int main()
{	
	//** USER INPUTS THE SETS **

	// Set A
	a=0;
	cout << "Enter set A: " << endl;
	while (a < 20)
	{
		cin >> A[a];
		a++;
	}

	cout << "\n";
	
	b=0;
	// Set B
	cout << "Enter set B: " << endl;
	while(b < 20)
	{
		cin >> B[b];
		b++;
	}
	
	cout << "\n";

	c= 0;
	// Set C
	cout << "Enter set C: " << endl;
	while(c < 20)
	{
		cin >> C[c];
		c++;
	}

	cout << "\n";

	//** DISPLAY THE SETS A, B, C **

	// Display A
	cout << "Set A: " << endl;
	for (a = 0; a < 20; a++)
	{
		cout << A[a] << ", ";	
	}
	
	cout << "\n";
	
	// Display B
	cout << "Set B: " << endl;
	for (b = 0; b < 20; b++)
	{
		cout << B[b] << ", ";	
	}
	
	cout << "\n";

	// Display C
	cout << "Set C: " << endl;
	for (c = 0; c < 20; c++)
	{
		cout << C[c] << ", ";	
	}

	cout << "\n";

	return 0;
}

[tummychow]

Just tell them to enter 21 to quit. If they enter 21, end the loop.