用c语言数组进行3元3次多项式的存储和加法

三元三次多项式可以表示为：

f(x,y,z) = a0 + a1 * x + a2 * y + a3 * z + a4 * x^2 + a5 * x * y + a6 * x * z + a7 * y^2 + a8 * y * z + a9 * z^2 + a10 * x^3 + a11 * x^2 * y + a12 * x^2 * z + a13 * x * y^2 + a14 * x * y * z + a15 * x * z^2 + a16 * y^3 + a17 * y^2 * z + a18 * y * z^2 + a19 * z^3

可以使用一个一维数组来存储这些系数，数组的下标表示各项的次数，例如：

coefficients[0] = a0
coefficients[1] = a1
coefficients[2] = a2
coefficients[3] = a3
coefficients[4] = a4
coefficients[5] = a5
coefficients[6] = a6
coefficients[7] = a7
coefficients[8] = a8
coefficients[9] = a9
coefficients[10] = a10
coefficients[11] = a11
coefficients[12] = a12
coefficients[13] = a13
coefficients[14] = a14
coefficients[15] = a15
coefficients[16] = a16
coefficients[17] = a17
coefficients[18] = a18
coefficients[19] = a19

可以定义一个结构体来封装这个数组和多项式的信息：

typedef struct {
double coefficients[20];
} Polynomial3;

可以定义一个函数来实现多项式的加法，例如：

Polynomial3 addPolynomials3(Polynomial3 p1, Polynomial3 p2) {
Polynomial3 result;
int i;
for (i = 0; i < 20; i++) {
result.coefficients[i] = p1.coefficients[i] + p2.coefficients[i];
}
return result;
}

这个函数接受两个三元三次多项式作为参数，返回它们的和。函数通过遍历两个多项式的系数数组，将对应项相加，得到新的系数数组。