创建一个类，重载运算符实现多项式的加，减，乘运算

唉，我太弱了，这么个简单的东西，还是用数组写的，却因为各种错误，弄了一个晚上，C++还得好好学啊，各种语法，要弄清楚。

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <iomanip>
#include <cstring>

using namespace std;

class Polynomial
{
public:
    Polynomial(int  = 0);
    friend istream & operator >> (istream & input, Polynomial & pl);
    friend ostream & operator << (ostream & output, Polynomial & pl);
    Polynomial & operator += (Polynomial & add);
    Polynomial & operator -= (Polynomial & add);
    Polynomial & operator - (Polynomial & add);
    Polynomial & operator * (Polynomial &);
    Polynomial & operator + (Polynomial & add);
    Polynomial & operator *= (Polynomial &);
    Polynomial & operator = (Polynomial & right);
    Polynomial & test(Polynomial & right);
private:
    int *a;
    int size, num;
};

Polynomial & Polynomial::operator *= (Polynomial & mu)
{
    Polynomial b, c;
    c = *this; b = *this;
    for (int j=0,r=0; j<b.num;++j,r+=2)
    {
        (*this).a[r]+=mu.a[0]; (*this).a[r+1]*=mu.a[1];
    }
    for (int i=1,k=2;i<mu.num;++i,k+=2)
    {
        for (int j=0,r=0; j<b.num;++j,r+=2)
        {
            b.a[r]+=mu.a[k];
            b.a[r+1]*=mu.a[k+1];
        }
        *this += b;
        b = c;
    }
    return *this;
}
Polynomial & Polynomial::operator * (Polynomial & mu)
{
    Polynomial b, c;
    c = *this; b = *this;
    for (int j=0,r=0; j<b.num;++j,r+=2)
    {
        (*this).a[r]+=mu.a[0]; (*this).a[r+1]*=mu.a[1];
    }
    for (int i=1,k=2;i<mu.num;++i,k+=2)
    {
        for (int j=0,r=0; j<b.num;++j,r+=2)
        {
            b.a[r]+=mu.a[k];
            b.a[r+1]*=mu.a[k+1];
        }
        *this += b;
        b = c;
    }
    return *this;
}

Polynomial & Polynomial::operator = (Polynomial & right)
{
    if (&right != this)
    {
        delete [] a;
        size = right.size;
        num = right.num;
        a = new int[size];
        for (int i = 0; i < size; ++i)
            a[i]=right.a[i];
    }
    else
        cout<<"Attempted assignment of a polynomial to itself" << endl;
    return *this;
}

Polynomial & Polynomial::operator -= (Polynomial & add)
{
    int number = add.num, mrk = 0;
    int cosize = add.size; int * q = new int[cosize];
    for (int d=0;d<cosize;++d) q[d]=add.a[d];
    for (int i = 0, s = 0; i < number; ++i, s+=2)
    {
        mrk = 0;
        for (int j = 0, k = 0; j < num; ++j,k+=2)
        {
            if (q[s]==a[k])
            {
                mrk = 1;
                a[k+1]-=q[s+1];
                q[s+1]=0;
            }
        }
        if (!mrk)
        {
            int *p = new int[size+2];
            for (int d=0;d<size;d++)
                p[d]=a[d];
            p[size] = q[s];
            p[size+1] = -q[s+1];
            q[s+1]=0;
            a = p;
            num++;
            size+=2;
        }
    }
    return *this;
}
Polynomial & Polynomial::operator - (Polynomial & add)
{
    int number = add.num, mrk = 0;
    int cosize = add.size; int * q = new int[cosize];
    for (int d=0;d<cosize;++d) q[d]=add.a[d];
    for (int i = 0, s = 0; i < number; ++i, s+=2)
    {
        mrk = 0;
        for (int j = 0, k = 0; j < num; ++j,k+=2)
        {
            if (q[s]==a[k])
            {
                mrk = 1;
                a[k+1]-=q[s+1];
                q[s+1]=0;
            }
        }
        if (!mrk)
        {
            int *p = new int[size+2];
            for (int d=0;d<size;d++)
                p[d]=a[d];
            p[size] = q[s];
            p[size+1] = -q[s+1];
            q[s+1]=0;
            a = p;
            num++;
            size+=2;
        }
    }
    return *this;
}

Polynomial & Polynomial::operator += (Polynomial & add)
{
    int number = add.num, mrk = 0;
    int cosize = add.size; int * q = new int[cosize];
    for (int d=0;d<cosize;++d) q[d]=add.a[d];
    for (int i = 0, s = 0; i < number; ++i, s+=2)
    {
        mrk = 0;
        for (int j = 0, k = 0; j < num; ++j,k+=2)
        {
            if (q[s]==a[k])
            {
                mrk = 1;
                a[k+1]+=q[s+1];
                q[s+1]=0;
            }
        }
        if (!mrk)
        {
            int *p = new int[size+2];
            for (int d=0;d<size;d++)
                p[d]=a[d];
            p[size] = q[s];
            p[size+1] = q[s+1];
            q[s+1]=0;
            a = p;
            num++;
            size+=2;
        }
    }
    return *this;
}

Polynomial & Polynomial::operator + (Polynomial & add)
{
    int number = add.num, mrk = 0;
    Polynomial & mi = *this;
    int cosize = add.size; int * q = new int[cosize];
    for (int d=0;d<cosize;++d) q[d]=add.a[d];
    for (int i = 0, s = 0; i < number; ++i, s+=2)
    {
        mrk = 0;
        for (int j = 0, k = 0; j < mi.num; ++j,k+=2)
        {
            if (q[s]==mi.a[k])
            {
                mrk = 1;
                mi.a[k+1]+=q[s+1];
                q[s+1]=0;
            }
        }
        if (!mrk)
        {
            int *p = new int[mi.size+2];
            for (int d=0;d<mi.size;d++)
                p[d]=mi.a[d];
            p[mi.size] = q[s];
            p[mi.size+1] = q[s+1];
            q[s+1]=0;
            mi.a = p;
            mi.num++;
            mi.size+=2;
        }
    }
    return mi;
}

ostream & operator << (ostream & output, Polynomial & pl)
{
    for (int i = 0, j = 0; i < pl.num; ++i)
    {
        if (pl.a[j+1]==0)
        {
            output << "0 0 "; j+=2; continue; 
        }
        output << pl.a[j+1] << " " << pl.a[j] << " ";
        j+=2;
    }
    output << endl;
    return output;
}

istream & operator >> (istream & input, Polynomial & pl)
{
    cout << "input the number of Polynomial terms: ";
    input >> pl.num;
    pl.size = pl.num * 2;
    pl.a = new int[pl.size];
    int s, t;
    for (int i = 0, j = 0; i < pl.num;)
    {
        input >> s >> t; 
        pl.a[j] = t; pl.a[j+1] = s;
        i++; j+=2;
    }
    return input;
}

Polynomial::Polynomial(int n)
    :num(n)
{
    size = num * 2;
    a = new int[size];
}

int main(void)
{
    Polynomial poly1, poly2, poly;
    freopen("in", "r", stdin);

    cin >> poly1;
    cout << endl;
    cin >> poly2;
    cout << endl; 

/*    poly = poly1 + poly2;
    cout << poly;

    poly1 -= poly2;
    poly = poly1;
    cout << poly;
*/
    poly = poly1 * poly2;
    cout << poly;

    return 0;
}

　　这个程序写得不好，重载运算符+，-，*和+=，-=，*=的代码是一样的，以后再改一下。而且很多地方，效率很低，很繁琐。

　　总结一下：因为在一个成员函数里面重复定义了一个变量，导致怎么也不对。最后没办法，现学gdb调试了，唉，这才发现错误，以后写代码的时候要过脑子，别想怎么写就怎么写，想想为什么这么写，认真一点儿，就会节约很多时间！当程序出现错误的时候，你的信念不应该是：我的程序是对的啊，怎么看怎么对。而应该是这样的：我的程序肯定在某个地方出错了，然后一行一行地检查。这样才会尽快找出错误。