char to int

Hello!

I am using a book to study from and I was wondering how exactly this line of code works:

result = (number[0] + number[1] + number[2] + number[3] + number[4] -4*'0');


specifically

+ number[4] -4*'0'




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#include <iostream>
using namespace std;
int main()
{
	char
		number[5], word[5], ch;
	int
		result, result2;

	cout <<
		"Enter a 4-digit number:";
	cin >> number;
	
	cout << int(char(2));
	result = (number[0] + number[1] + number[2] + number[3] + number[4] -4*'0');
	cout << "\Sum of digits =" << result;

	cout <<
		"\nEnter a 4-letter word:";
	cin >> word;

	ch = (word[0] + word[1] + word[2] + word[3]) / 4;
	cout <<
		"\nAverage char =" << ch << endl;
	system(
		"pause");
	return
		0;
}
http://www.asciitable.com/

What is the decimal value for 0?
There are several errors in that code.
This line:
 
result = (number[0] + number[1] + number[2] + number[3] + number[4] -4*'0');
should instead be:
 
result = (number[0] + number[1] + number[2] + number[3] - 4*'0');


The reason for the - 4*'0' is that the line is a simplification of this:
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    result =   number[0] - '0'
             + number[1] - '0' 
             + number[2] - '0' 
             + number[3] - '0';


Also I think this line:
 
    cout << int(char(2));
would make more sense and be more useful in the context, written like this:
 
    cout << int('2');


At line 16, "\Sum of digits =" should be "\nSum of digits ="
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