C++PrimerPlus中文第六版第7章编程练习答案

1、

#include<iostream>
using namespace std;

double computeHarmonicMean(double x, double y);
int main()
{
    double x, y;
    cout << "Enter two numbers(x!=0 and y!=0): ";
    bool valid;
    valid = (bool)(cin >> x >> y);
    while (!valid)
    {
        cin.clear();
        while (cin.get() != '\n');
        cout << "Enter invalid! enter again!\n";
        cout << "Please enter two numbers(x!=0 and y!=0): ";
        valid = (bool)(cin >> x >> y);
    }
    while (x != 0 and y != 0)
    {
        cout <<"Harmonic mean: " << computeHarmonicMean(x, y) << endl;
        cout << "Enter two numbers(x!=0 and y!=0): ";
        valid = (bool)(cin >> x >> y);
        while (!valid)
        {
            cin.clear();
            while (cin.get() != '\n');
            cout << "Enter invalid! enter again!\n";
            cout << "Please enter two numbers(x!=0 and y!=0): ";
            valid = (bool)(cin >> x >> y);
        }
    }

    cout << "x==0 or y==0 holds to quit\n";


}

double computeHarmonicMean(double x, double y)
{
    return 2.0 * x * y / (x + y);
}

2、

#include<iostream>
using namespace std;

const int Size = 10;
int getScore(double* score, int n);
void showScore(double* score, int n);
void compute_showAve(double* score, int n);

int main()
{
    double golfScore[Size];
    int getNumber = getScore(golfScore, Size);
    showScore(golfScore, getNumber);
    compute_showAve(golfScore, getNumber);

}

void compute_showAve(double* score, int n)
{
    double sum = 0;
    for (int i = 0; i < n; i++)
        sum += score[i];
    cout << "Ave is " << sum / n << endl;
}
void showScore(double* score, int n)
{
    for (int i = 0; i < n; i++)
        cout << "score[" << i << "]=" << score[i] << endl;
}
int getScore(double* score, int n)
{
    double x;
    int i = 0;
    cout << "Enter the " << i + 1 << "th score(negative or not number to quit): ";
    while (cin >> x and x >= 0 and i < n)
    {
        cout << "Enter the " << i + 1 << "th score(negative or not number to quit): ";
        *(score+i) = x;
        i++;
    }
    cout << "Entering up to " << n << " numbers or error occurred, the input process is to end. "
        << i << " numbers have been gotten.\n";
    return i;
}

3、

#include<iostream>
using namespace std;

struct box
{
    char maker[40];
    float height;
    float width;
    float length;
    float volume;
};

void showBox(box crate);
void setVolume(box* crate);
int main()
{
    box crate = { "lenovo", 0.6, 0.2, 0.35, 0.00};
    showBox(crate);
    setVolume(&crate);
    showBox(crate);
}
void setVolume(box* crate)
{
    crate->volume = (crate->height) * (crate->width) * (crate->length);
}
void showBox(box crate)
{
    cout << "maker: " << crate.maker << endl;
    cout << "height: " << crate.height << endl;
    cout << "width: " << crate.width << endl;
    cout << "length: " << crate.length << endl;
    cout << "volume: " << crate.volume << endl;
}

4、

#include<iostream>
using namespace std;

int main()
{
    double prob = 1;
    for (int i = 0; i < 5; i++)
    {
        prob *= (47 - i) / (1 + i);
    }
    prob *= 27;
    cout.precision(10);
    cout.setf(ios::fixed);
    cout << "The probability of first prize is: " << 1/prob * 100 << "%\n";
}

5、

#include<iostream>
using namespace std;

long long getFactorial(int n);

int main()
{
    int n;
    long long factorial;
    cout << "Enter n(negative or NoN to quit): ";
    while (cin >> n and n >= 0)
    {
        factorial = getFactorial(n);
        cout << "the factorial of " << n << " is " << factorial << endl;
        cout << "Enter n(negative or NaN to quit): ";
    }
    cout << "n<0 or invalid input for n to quit.\n";
}

long long getFactorial(int n)
{
    if (n == 0 or n == 1)
    {
        return 1;
    }
    else
    {
        return n * getFactorial(n - 1);
    }
}

6、

 

#include<iostream>
using namespace std;

const int Size = 10;

int Fill_array(double* ar, int n);
void Show_array(const double ar[], int n);
void Reverse_array(double* begin, double* end);

int main()
{
    double dar[Size];
    int fillNum;
    fillNum = Fill_array(dar, Size);
    Show_array(dar, fillNum);
    Reverse_array(dar, dar+fillNum-1);
    Show_array(dar, fillNum);
    Reverse_array(dar + 1, dar + fillNum-2);
    Show_array(dar, fillNum);
}
void Reverse_array(double* begin, double* end)
{
    if (begin >= end)
    {
        cout << "quit(Because the length of the array to be flipped is less than or equal to 0)\n";
        return;
    }
    else
    {
        double temp;
        while (begin < end)
        {
            temp = *begin;
            *begin = *end;
            *end = temp;
            begin++; end--;
        }
    }
        
        
}
void Show_array(const double ar[], int n)
{
    for (int i = 0; i < n; i++)
        cout << "ar[" << i << "]=" << ar[i] << endl;
}
int Fill_array(double* ar, int n)
{
    int i = 0;
    cout << "Enter the " << i + 1 << "th number of the array(NaN to quit): ";
    while (cin >> *(ar + i++) and i < n)
    {
        cout << "Enter the " << i+1 << "th number of the array(NaN to quit): ";
    }
    cout << "Filling quit by up to " << i << " numbers filled or NaN entered.\n"
        << i << " numbers have been filled.\n";
    return i;
}

7、

#include<iostream>
using namespace std;

const int Max = 5;

double* fill_array(double* begin, double* end);
void show_array(const double* begin, const double* end);
void revalue(double r, double* begin, double* end);

int main()
{
    double properties[Max];
    double* end = fill_array(properties, properties+Max);
    show_array(properties, end);
    if (end > properties)
    {
        cout << "Enter revaluation factor: ";
        double factor;
        while (!(cin >> factor))
        {
            cin.clear();
            while (cin.get() != '\n');
            cout << "Bad input; Please enter a number: ";
        }
        revalue(factor, properties, end);
        show_array(properties, end);
    }
    cout << "Done.\n";
}

void revalue(double r, double* begin, double* end)
{
    while (begin < end)
    {
        *begin *= r;
        begin++;
    }
}
void show_array(const double* begin, const double* end)
{
    for (int i = 0; begin + i != end; i++)
    {
        cout << "properties[" << i << "]=" << *(begin + i) << endl;
    }
}
double* fill_array(double* begin, double* end)
{
    int i = 0;
    while ((begin+i) < end)
    {
        cout << "Enter value #" << i + 1<<": ";
        cin >> *(begin + i);
        if (!cin or *(begin+i) < 0)
        {
            cin.clear();
            while (cin.get() != '\n');
            cout << "Bad input; input process terminated.\n";
            break;
        }
        i++;
    }
    return begin + i;
}

8、

#include<iostream>
using namespace std;

const int Seasons = 4;

const char* Snames[Seasons] = { "Spring", "Summer", "Fall", "Winter" };

struct expense
{
    double expenses[Seasons];
};

void fill(double* enpenses);
void fill(expense* exp);
void show(double expenses[]);
void show(expense* exp);

int main()
{
    double expenses[Seasons];
    fill(expenses);
    show(expenses);

    expense exp;
    fill(&exp);
    show(&exp);
}

void show(expense* exp)
{
    double total = 0.0;
    for (int i = 0; i < Seasons; i++)
    {
        cout << Snames[i] << ": $" << exp->expenses[i] << endl;
        total += exp->expenses[i];
    }
    cout << "Total Expenses: $" << total << endl;
}
void fill(expense* exp)
{
    for (int i = 0; i < Seasons; i++)
    {
        cout << "Enter " << Snames[i] << " expenses: $";
        cin >> exp->expenses[i];
    }
}

void show(double expenses[])
{
    double total = 0.0;
    for (int i = 0; i < Seasons; i++)
    {
        cout << Snames[i] << ": $" << expenses[i] << endl;
        total += expenses[i];
    }
    cout << "Total Expenses: $" << total << endl;
}
void fill(double* expenses)
{
    for (int i = 0; i < Seasons; i++)
    {
        cout << "Enter " << Snames[i] << " expenses: ";
        cin >> expenses[i];
    }
}

9、

#include<iostream>
using namespace std;

const int SLEN = 30;

struct student
{
    char fullname[SLEN];
    char hobby[SLEN];
    int ooplevel;
};

int getinfo(student pa[], int n);
void display1(student st);
void display2(student* ps);
void display3(const student pa[], int n);

int main()
{
    cout << "Enter class size: ";
    int class_size;
    while (!(cin >> class_size))
    {
        cin.clear();
        while (cin.get() != '\n');
        cout << "class size invalid! please enter again: ";
    }
    cin.clear();
    while (cin.get() != '\n');

    student* ptr_stu = new student[class_size];
    int entered = getinfo(ptr_stu, class_size);
    for (int i = 0; i < entered; i++)
    {
        display1(ptr_stu[i]);
        display2(&ptr_stu[i]);
    }
    display3(ptr_stu, entered);
    delete[] ptr_stu;
    cout << "Done.\n";

}
void display3(const student pa[], int n)
{
    for (int i = 0; i < n; i++)
    {
        cout << "student #" << i + 1 <<": " << endl;
        cout << "fullname: " << pa[i].fullname << endl;
        cout << "hobby: " << pa[i].hobby << endl;
        cout << "ooplevel: " << pa[i].ooplevel << endl;
    }
}
void display2(student* ps)
{
    cout << "display2:\n";
    cout << "fullname: " << ps->fullname << endl;
    cout << "hobby: " << ps -> hobby << endl;
    cout << "ooplevel: " << ps->ooplevel << endl;
}
void display1(student st)
{
    cout << "display1:\n";
    cout << "fullname: " << st.fullname << endl;
    cout << "hobby: " << st.hobby << endl;
    cout << "ooplevel: " << st.ooplevel << endl;
}
int getinfo(student pa[], int n)
{
    int i;
    for (i = 0; i < n; i++)
    {
        cout << "Enter #" << i + 1 << " student's info:\n";
        cout << "fullname: ";
        cin.getline(pa[i].fullname, SLEN);
        if (strlen(pa[i].fullname) == 0)
        {
            cout << "fullname is empty, quit!\n";
            break;
        }
        cout << "hobby: ";
        cin.getline(pa[i].hobby, SLEN);
        cout << "ooplevel: ";
        cin >> pa[i].ooplevel;
        cin.clear();
        while (cin.get() != '\n');
    }
    cout << i << " students' info have been gotten.\n";
    return i;
}

10、

#include<iostream>
using namespace std;

double add(double x, double y);
double sub(double x, double y);
double mul(double x, double y);

double calculate(double x, double y, double (*pf)(double, double));

int main()
{
    double x, y;
    cout << "Enter x and y: ";

    double (*pf[3])(double, double) = { add, sub, mul };
    while (cin >> x >> y)
    {
        for (int i = 0; i < 3; i++)
            cout << "the result of calculate is: " << calculate(x, y, pf[i]) << endl;
        cout << "Enter x and y: ";
    }

    /*    
    while (cin >> x >> y)
    {
        cout << "The sum of x and y is: " << calculate(x, y, add) << endl;
        cout << "The difference between x and y is: " << calculate(x, y, sub) << endl;
        cout << "The multiply of x and y is: " << calculate(x, y, mul) << endl;
        cout << "Enter x and y: ";
    }
    */

}

double calculate(double x, double y, double (*pf)(double, double))
{
    return (*pf)(x,y);
}
double mul(double x, double y)
{
    return x* y;
}
double sub(double x, double y)
{
    return x - y;
}
double add(double x, double y)
{
    return x + y;
}