全部。我正在尝试建立一个程序,根据 X 的用户输入来计算多项式。我想要的程序的另一部分是将这些多项式加在一起。我正在使用二维数组来执行此操作。您认为编写评估函数的最佳方式是什么。已经为此工作了几个小时,但我仍然不太确定该怎么做。提前致谢。
多项式.h
#ifndef POLYNOMIAL_H
#define POLYNOMIAL_H
#include <iostream>
using namespace std;
#define MAX 100
class Polynomial {
friend ostream &operator<< (ostream &, const Polynomial &);
public :
Polynomial ();
void enterTerms();
int evaluate(Polynomial p, int x);
Polynomial operator +(const Polynomial & );
private :
int terms[MAX][2]; //either static size(MAX rows) or use "new" for dynamic allocation
int n; //number of terms
};
#endif
多项式.cpp
#include "polynomial.h"
using namespace std;
ostream &operator<< (ostream & out, const Polynomial & p){
for ( int i = 0 ; i < p.n ; i++ ){
if ( i == p.n - 1 )//last term does not have + appended
out << p.terms[i][0] <<"x^"<<p.terms[i][1]<<endl;
else
out << p.terms[i][0]<<"x^"<<p.terms[i][1]<<" + ";
}
return out;
}
Polynomial :: Polynomial(){
for ( int i = 0; i < MAX; i++ ){
terms[i][0] = 0;
terms[i][1] = 0;
}
}
void Polynomial :: enterTerms(){//enterTerms() not in constructor so that no prompt for entering
//terms while doing + - etc., they also produce Poylnomial instance (i.e. invoke constructor)
int num;
cout<<"enter number of terms in polynomial\n";
cin >> num;
n = num >= 0 ? num : 1;
cout << "enter coefficient followed by exponent for each term in polynomial\n";
for ( int i = 0; i < n ; i++)
cin >> terms[i][0] >> terms[i][1] ;
}
Polynomial Polynomial :: operator + ( const Polynomial & p ){
Polynomial temp, sum;
temp.n = n + p.n;
int common = 0;
// first write sum as concatenation of p1 and p2
for ( int i = 0 ; i < n ; i++ ){
temp.terms[i][0] = terms[i][0];
temp.terms[i][1] = terms[i][1];
}
//notice j and k for traversing second half of sum, and whole p2 resp
for ( int j = n, k = 0; j < n + p.n, k < p.n ; j++, k++ ){
temp.terms[j][0] = p.terms[k][0];
temp.terms[j][1] = p.terms[k][1];
}
for ( int l = 0; l < temp.n - 1 ; l++ ){ // 0 to 1 less than length
for ( int m = l + 1 ; m < temp.n ; m++ ){ // 1 more than l to length,so that compared pairs are non redundant
if( temp.terms[l][1] == temp.terms[m][1] ){
common++; //common terms reduce no. of terms in sum (see sum.n decl)
temp.terms[l][0] += temp.terms[m][0]; //coefficients added if exponents same
temp.terms[m][0] = 0;
}
}
}
sum.n = temp.n - common; //if you place it above, common taken as 0 and sum.n is same as temp.n (logical error)
//just to debug, print temporary array
cout << endl << temp;
for ( int q = 0, r = 0; q < temp.n; q++ ){
if ( temp.terms[q][0] == 0 )
continue;
else{
sum.terms[r][0] = temp.terms[q][0];
sum.terms[r][1] = temp.terms[q][1];
r++;
}
}
cout << endl << sum;
return sum;
}
int Polynomial :: evaluate(Polynomial p, int x)
{
Polynomial terms;
return 0;
}
int main()
{
Polynomial p1 , p2;
p1.enterTerms();
p2.enterTerms();
cout << "Please enter the value of x:" << endl;
cin >> x;
//evaluate(p1);
//evaluate(p2);
p1 + p2;
system("PAUSE");
//cin.get();
return 1;
}
最佳答案
请考虑更简单的数据结构。一种常见的方法是使用单个数组,其中索引是 x 的幂。只在不存在此类术语的地方使用零。然后 x^3 + 2*x + 1
写成 {1, 2, 0, 1}
,因为没有 x^2
。还要注意相反的顺序,因为 p[0]
代表 x^0
。这极大地简化了加法等操作。
至于评价,想想方程就知道了。如果您的多项式是 x^2 + 3*x + 5
,并且您想要计算 x=7,您会怎么做?从 0 次幂开始,将每一项累加到一个变量中。
关于c++ - 在 C++ 中评估基于矩阵的多项式的最佳方法,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19299969/