5.6

#define  _CRT_SECURE_NO_WARNINGS 
#include<iostream>
using namespace std;
int main()
{
	const int Years = 3;
	const int Months = 12;
	const char* Month[Months] =
	{
		"January",
		"February",
		"Match",
		"April",
		"May",
		"June",
		"July",
		"August",
		"September",
		"October",
		"November",
		"December"
	};
	int sales_volume[Years][Months];
	int sum[3] = {0,0,0};
	for (int k = 0; k< Years; k++)
	{
		cout << "In the " << k + 1 << " year,the out sales volume of books is :" << endl;
		for (int i = 0; i < Months; i++)
		{
			cout << "Enter the sales volume in " << Month[i] << ':';
			cin >> sales_volume[k][i];
			sum[k] += sales_volume[k][i];
		}
		cout << "This year out whole sales volume is " << sum[k] << endl;
	}
	
	cout << "And the 3 years we sold " << sum[0] + sum[1] + sum[2] << " altogether!" << endl;
	return 0;
}