能够按照指数降序排列建立并输出多项式；能够完成两个多项式的相加、相减和相乘，并将结果输出。用C语言写

在C语言中，要实现这样的多项式操作，你可以创建一个结构体表示多项式项，包括系数和指数。这里是一个简单的例子，展示了如何创建结构体、添加元素、以及实现加法、减法和乘法的基本功能： ```c #include <stdio.h> #include <stdlib.h> // 定义多项式项结构体 typedef struct { double coefficient; int exponent; } Term; // 添加多项式项 void addTerm(Term* poly, double coef, int exp) { Term newTerm = {coef, exp}; if (poly == NULL) { poly = &newTerm; } else { Term* last = poly; while (last->exponent > exp) last = last->next; if (last->exponent == exp) last->coefficient += coef; else { Term* newNode = malloc(sizeof(Term)); newNode->coefficient = coef; newNode->exponent = exp; newNode->next = last->next; last->next = newNode; } } } // 创建并打印多项式 void createPolynomial(Term** poly, int numTerms, ...) { va_list args; va_start(args, numTerms); for (int i = 0; i < numTerms; ++i) { double coef = va_arg(args, double); int exp = va_arg(args, int); addTerm(poly, coef, exp); } va_end(args); Term* curr = *poly; printf("Polynomial: "); while (curr != NULL) { printf("%.2f x^%d + ", curr->coefficient, curr->exponent); curr = curr->next; } printf("\n"); } // 相加、相减多项式 Term* addSubtract(Term* poly1, Term* poly2, char op) { Term* result = NULL; Term* temp1 = poly1, *temp2 = poly2; while (temp1 != NULL || temp2 != NULL) { double coef1 = temp1 ? temp1->coefficient : 0; double coef2 = temp2 ? temp2->coefficient : 0; switch(op) { case '+': coef1 += coef2; break; case '-': coef1 -= coef2; break; } // 创建新节点 Term* newNode = malloc(sizeof(Term)); newNode->coefficient = coef1; newNode->exponent = temp1 ? temp1->exponent : temp2->exponent; // 连接新节点到结果链表 if (result == NULL) { result = newNode; } else { Term* last = result; while (last->exponent > newNode->exponent) last = last->next; last->next = newNode; } // 移动到下一个待处理的项 temp1 = temp1 ? temp1->next : NULL; temp2 = temp2 ? temp2->next : NULL; } return result; } // 输出多项式 void printPolynomial(Term* poly) { Term* curr = poly; printf("Result (after %s): ", op == '+' ? "addition" : "subtraction"); while (curr != NULL) { printf("%.2f x^%d + ", curr->coefficient, curr->exponent); curr = curr->next; } printf("\n"); } int main() { Term* poly1 = NULL, *poly2 = NULL; createPolynomial(&poly1, 2, 2.0, 3, 4.0, 5); // 示例多项式1: 2x^2 + 3x + 4 createPolynomial(&poly2, 2, -1.5, 0); // 示例多项式2: -1.5x^0 char op = '+'; // 改变此变量可以进行加法或减法运算 Term* result = addSubtract(poly1, poly2, op); printPolynomial(result); free(result); return 0; } ``` 注意，这只是一个基本的实现，实际项目中可能需要考虑更多的边界情况和错误处理。此外，乘法的实现会更为复杂，通常会使用递归展开或者动态规划技巧。