Caeser Cipher Program. Help wanted.

[Wulfinite]

So I have basically learnt this for fun on youtube, and for the most part I can understand what the guy had done, but there are some things I do not quite get.

#include <iostream>
#include <string>
using namespace std;

int main()
{
	string input;
	int count = 0;
	int l;

	cout << "Enter a sentence: \n" << endl;
	getline(cin, input);

	l = (int)input.length();

	for (count = 0; count < l; count++)
	{
		if (isalpha(input[count]))
		
			input[count] = tolower(input[count]);
			for (int i = 0; i < 13; i++)
			{
				if (input[count] == 'z')
				{
					input[count] = 'a';
				}
				else
				{
					input[count]++;
				}
			}
		}
	system("Color A");
	cout << endl;
	cout << "Encryption: " << input << endl;
	cout << endl;
	system("PAUSE");
	return 0;

	}

PROBLEM:
Line 18 to 29.

I don't quite understand what '(input[count])' does on line 18. In fact, I'm not sure whats happening with anything that has the square brackets '[]'

Please help me to understand with the square brackets imply and what they do? I really need to understand this. Sounds very interesting.

Could you also explain whats happening on line 14 as well? Much appreciated.

[MiiNiPaa]

the square brackets imply and what they do?

Square brackets are used to access array element:
input[0] is first element, input[1] is next and so on. input[i] is elements with index i.

whats happening on line 14

i is assigned length of string. THere is cast here (int) to suppress warnings (and it is here because whoever wrote this code choose variable types poorly)

[Wulfinite]

So string count is acted like an array? And every character is indexed?

[MiiNiPaa]

String is array of characters by its definition.

[48T7M4Gy]

http://www.cplusplus.com/doc/tutorial/arrays/