C++ Primer Plus第五章课后习题总结

1.编写一个要求用户输入两个整数的程序。该程序将计算并输出这两个整数之间（包括这两个整数）所有整数的和。这里假设先输入较小的整数。例如，如果用户输入的是2和9，则程序将指出2~9之间所有整数的和为44。

#include <iostream>

int main()
{
    using namespace std;
    int fInt, sInt;
    int sum = 0;
    cout << "Enter two integers:" << endl;
    cout << "The first integer :";
    cin >> fInt;
    cout << "The second integer :";
    cin >> sInt;

    for (int i = fInt; i <= sInt; i++) {
        sum += i;
    }
    cout << "Sum between the first integer and the second integer: ";
    cout << sum;
    return 0;
}

2.使用array对象（而不是数组）和long double（而不是long long）重新编写程序清单5.4，并计算100！的值。

// 5.4formore.cpp -- more looping with for
#include <iostream>
const int ArSize = 16; // example of external declaration
int main()
{
    long long factorials[ArSize];
    factorials[1] = factorials[0] = 1LL;
    for (int i = 2; i < ArSize; i++)
    factorials[i] = i * factorials[i-1];
    for (int i = 0; i < ArSize; i++)
    std::cout << i << "! = " << factorials[i] << std::endl;
    return 0;
}

#include <iostream>
#include <array>

const int ArSize = 16;
int main()
{
    using namespace std;
    array<long double, ArSize> factorials;
    factorials[1] = factorials[0] = 1.0;
    for (int i = 2; i < ArSize; i++)
        factorials[i] = i * factorials[i - 1];
    for (int i = 0; i < ArSize; i++)
        cout << i << "! = " << factorials[i] << endl;
    return 0;
}