求C++大神指教一下，给点意见或一些编程步骤

Question

第一个还有点看得懂，但后面的就不太懂了

Answer 1

1. a)

    unsigned int x;
    unsigned int jc = 1;
    cout << "请输入一个非负整数：" << endl;
    cin >> x;
    while (x)
    {
        jc *= x;
        x--;
    }
    cout << "x!=" << jc << endl;

1. b)

    int n = 1;
    int jc = 1;
    float e = 0.0;
    int i = 0;
    cout << "请输入求和项数：" << endl;
    cin >> n;
    while (i < n)
    {
        if (i == 0)
            jc = 1;
        else
            jc *= i;
        i++;
        e += 1.0 / jc;
    }
    cout << "数学常量e=" << e << endl;

第三个类似的，不多说