用C语言写多项式相加减

在C语言中，我们可以使用数组来存储多项式的系数及其对应的变量次数，然后编写函数来进行多项式的加法和减法操作。这里提供一个简单的示例，仅支持一次、二次和常数项的加减运算：

#include <stdio.h>
#include <stdlib.h>

typedef struct Polynomial {
    double* coefficients; // 数组存储系数
    int degree;            // 最高次幂
} Polynomial;

// 添加两个多项式
Polynomial add_poly(Polynomial poly1, Polynomial poly2) {
    if (poly1.degree != poly2.degree) {
        printf("两项多项式的度数不匹配，无法相加。\n");
        return poly1;
    }
    
    Polynomial result;
    result.degrees = poly1.degree + 1;
    result.coefficients = malloc(sizeof(double) * result.degrees);

    for (int i = 0; i <= poly1.degree; ++i) {
        result.coefficients[i] = poly1.coefficients[i] + poly2.coefficients[i];
    }

    return result;
}

// 减去两个多项式
Polynomial subtract_poly(Polynomial poly1, Polynomial poly2) {
    if (poly1.degree != poly2.degree) {
        printf("两项多项式的度数不匹配，无法相减。\n");
        return poly1;
    }
    
    Polynomial result;
    result.degrees = poly1.degree + 1;
    result.coefficients = malloc(sizeof(double) * result.degrees);

    for (int i = 0; i <= poly1.degree; ++i) {
        result.coefficients[i] = poly1.coefficients[i] - poly2.coefficients[i];
    }

    return result;
}

// 示例
void print_polynomial(Polynomial poly) {
    printf("多项式：");
    for (int i = poly.degree; i >= 0; --i) {
        printf("%.2f*x^%d + ", poly.coefficients[i], i);
    }
    printf("%.2fx^0\n", poly.coefficients[0]);
}

int main() {
    Polynomial p1 = { {1.5, 2.0}, 2 };
    Polynomial p2 = { {2.0, 1.0}, 2 };

    Polynomial sum = add_poly(p1, p2);
    Polynomial diff = subtract_poly(p1, p2);

    print_polynomial(sum);
    print_polynomial(diff);

    free(sum.coefficients);
    free(diff.coefficients);
    return 0;
}

这个代码首先定义了一个结构体`Polynomial`来存储多项式的系数和最高次幂。`add_poly`和`subtract_poly`函数分别实现了两个多项式的加法和减法。注意，这里的实现假设输入的多项式都是有公共的最高次幂，如果没有，需要额外检查。