我试图在C ++中添加两个多项式，我甚至迷失在哪里开始。因此，用户可以输入多项式的值，它们不需要按顺序排列。
例如它可以是： Poly 1：2x ^ 5 + 5x ^ 2 - 2x + 9 Poly 2：x ^ 2 + 0
我有系数和指数存储在类（对象）私有字段中。那么我会看看Poly 1中的第一个指数，首先搜索Poly 2的相同指数，如果找到则添加它们？然后继续第二个学期？
请求的代码:(注意：实现当前是错误的，我需要有关如何解决此问题的帮助。）
#include <cmath>
#include <iostream>
using namespace std;
class polynomial
{
public:
polynomial();
polynomial(int);
polynomial(int exponent[], int coefficient[], int);
~polynomial();
polynomial &operator = (const polynomial &obj);
int evaluate(double uservalue);
polynomial operator+(const polynomial &obj) const;
void operator-(const polynomial &obj) const;
void operator*(const polynomial &obj) const;
friend istream & operator>> (istream & in, polynomial &obj);
friend ostream & operator<< (ostream & out, const polynomial &obj);
friend void growone(polynomial &obj);
private:
int *coefficient;
int *exponent;
int size;
};
实施
polynomial polynomial::operator+(const polynomial &obj) const
{
bool matchFound = false;
polynomial tmp;
if (size >= obj.size) {
for (int i = 0; i < size; i++) {
if (i >= tmp.size) {
growone(tmp);
}
for(int y = 0; i < obj.size; i++) {
if (exponent[i] == obj.exponent[y]) {
tmp.coefficient[i] = (coefficient[i]+obj.coefficient[y]);
tmp.exponent[i] = exponent[i];
tmp.size++;
matchFound = true;
}
}
if (matchFound == false) {
tmp.coefficient[i] = coefficient[i];
tmp.exponent[i] = exponent[i];
tmp.size++;
}
matchFound = false;
}
} else {
}
return tmp;
}
答案 0 :(得分：1)
您并没有真正充分利用C ++的功能。一个很好的规则是，如果您将非智能指针用于任何东西，则应退后一步并重新考虑。
关于堆栈溢出C的大量问题都与指针问题无关：-）
我要补充的另一点是，实际上值得浪费少量的内存来大大简化代码。这样，我的意思是不要尝试创建稀疏数组来保存您的项（系数-指数对）。取而代之的是，让每个表达式最多保留每一项，并将未使用的项的系数简单地设置为零。除非您有类似4x99999999999999 + 3这样的表达式，否则占用的额外内存可能是值得的。
为此，我建议对指数从零开始的系数仅使用std::vector。指数实际上是由向量中的位置决定的。因此，表达式4x9 - 17x3 + 3将被存储为向量：
{3, 0, 0, -17, 0, 0, 0, 0, 0, 4}
0 <------- exponent -------> 9
实际上，由于系数都很好地排列在一起，因此使多项式相加和相减的任务非常容易。
因此，考虑到这一点，让我们介绍一个简化的类以显示其完成方式：
#include <iostream>
#include <vector>
using std::cout;
using std::vector;
using std::ostream;
class Polynomial {
public:
Polynomial();
Polynomial(size_t expon[], int coeff[], size_t sz);
~Polynomial();
Polynomial &operator=(const Polynomial &poly);
Polynomial operator+(const Polynomial &poly) const;
friend ostream &operator<<(ostream &os, const Polynomial &poly);
private:
std::vector<int> m_coeff;
};
默认构造函数（和析构函数）非常简单，我们只需确保初始化的多项式始终至少具有一项：
Polynomial::Polynomial() { m_coeff.push_back(0); }
Polynomial::~Polynomial() {}
constructor-from-array稍微复杂一点，因为我们希望尽早将用户的“一切”格式转换为易于使用的格式：
Polynomial::Polynomial(size_t expon[], int coeff[], size_t sz) {
// Work out largest exponent and size vector accordingly.
auto maxExpon = 0;
for (size_t i = 0; i < sz; ++i) {
if (expon[i] > maxExpon) {
maxExpon = expon[i];
}
}
m_coeff.resize(maxExpon + 1, 0);
// Fill in coefficients.
for (size_t i = 0; i < sz; ++i) {
m_coeff[expon[i]] = coeff[i];
}
}
现在，您将看到为什么我们决定不使用稀疏数组并将零指数放在向量的开头。 operator=和operator+都很简单，因为它们已经知道所有条件在哪里：
Polynomial &Polynomial::operator=(const Polynomial &poly) {
if (this != &poly) {
m_coeff.clear();
for (int coeff: poly.m_coeff) {
m_coeff.push_back(coeff);
}
}
return *this;
}
Polynomial Polynomial::operator+(const Polynomial &poly) const {
// Create sum with required size.
size_t thisSize = this->m_coeff.size();
size_t polySize = poly.m_coeff.size();
Polynomial sum;
if (thisSize > polySize) {
sum.m_coeff.resize(thisSize, 0);
} else {
sum.m_coeff.resize(polySize, 0);
}
// Do the actual sum (ignoring terms beyond each limit).
for (size_t idx = 0; idx < sum.m_coeff.size(); ++idx) {
if (idx < thisSize) sum.m_coeff[idx] += this->m_coeff[idx];
if (idx < polySize) sum.m_coeff[idx] += poly.m_coeff[idx];
}
return sum;
}
现在我们只需要使用输出功能和一条小的测试主线来完成此操作：
ostream &operator<< (ostream &os, const Polynomial &poly) {
bool firstTerm = true;
if (poly.m_coeff.size() == 1 && poly.m_coeff[0] == 0) {
os << "0";
return os;
}
for (size_t idx = poly.m_coeff.size(); idx > 0; --idx) {
if (poly.m_coeff[idx - 1] != 0) {
if (firstTerm) {
os << poly.m_coeff[idx - 1];
} else if (poly.m_coeff[idx - 1] == 1) {
os << " + ";
if (idx == 1) {
os << poly.m_coeff[idx - 1];
}
} else if (poly.m_coeff[idx - 1] == -1) {
os << " - ";
} else if (poly.m_coeff[idx - 1] < 0) {
os << " - " << -poly.m_coeff[idx - 1];
} else {
os << " + " << poly.m_coeff[idx - 1];
}
if (idx > 1) {
os << "x";
if (idx > 2) {
os << "^" << idx - 1;
}
}
firstTerm = false;
}
}
return os;
}
int main() {
int c1[] = {1, 2, 3, 4, 5};
size_t e1[] = {3, 1, 4, 0, 9};
Polynomial p1(e1, c1, (size_t)5);
cout << "Polynomial 1 is " << p1 << " (p1)\n";
int c2[] = {6, 7, 8};
size_t e2[] = {3, 7, 9};
Polynomial p2(e2, c2, (size_t)3);
cout << "Polynomial 2 is " << p2 << " (p2)\n";
Polynomial p3 = p1 + p2;
cout << "Polynomial 3 is " << p3 << " (p3 = p1 = p2);
}
输出（我将其重新格式化以显示类似的术语）将其显示为实际操作：
Polynomial 1 is 5x^9 + 3x^4 + x^3 + 2x + 4
Polynomial 2 is 8x^9 + 7x^7 + 6x^3
===================================
Polynomial 3 is 13x^9 + 7x^7 + 3x^4 + 7x^3 + 2x + 4