用单链表表示一元多项式，并实现输入、输出、加、减运算。…… 要求实现： (1)创建多项式 (2)多项式加法 (3)输出多项式 (4)多项式减法 用c语言 没有指数

在C语言中，我们可以使用结构体和单链表来表示一元多项式。首先，我们需要定义一个`Term`结构体来存储每个项，包括系数和变量（在这里我们假设是一次多项式，所以只有一个变量x）：

typedef struct {
    double coefficient; // 系数
    int variable;       // 变量，这里为1，因为我们只考虑一次多项式
} Term;

typedef struct Polynomial {
    Term* head;
    int degree;
} Polynomial;

接下来，我们实现一些基本操作：

1. **创建多项式** (`createPolynomial`):
- 初始化链表头节点，设置度为0。

   Polynomial* createPolynomial(double a) {
      Polynomial* poly = (Polynomial*)malloc(sizeof(Polynomial));
      poly->head = (Term*)malloc(sizeof(Term));
      poly->head->coefficient = a;
      poly->head->variable = 1;
      poly->degree = 1;
      return poly;
   }

2. **多项式加法** (`addPolynomials`):
- 遍历两个多项式的链表，累加对应系数的项。

   Polynomial* addPolynomials(Polynomial* p1, Polynomial* p2) {
      Polynomial* result = createPolynomial(0);
      Term* cur1 = p1->head;
      Term* cur2 = p2->head;
      while (cur1 && cur2) {
         if (cur1->coefficient > cur2->coefficient)
            result->head->coefficient += cur1->coefficient, cur1++;
         else
            result->head->coefficient += cur2->coefficient, cur2++;
      }
      while (cur1) {
         result->head->coefficient += cur1->coefficient;
         cur1++;
      }
      while (cur2) {
         result->head->coefficient += cur2->coefficient;
         cur2++;
      }
      result->degree = MAX(p1->degree, p2->degree);
      return result;
   }

3. **输出多项式** (`displayPolynomial`):
- 从头节点开始遍历并打印系数。

   void displayPolynomial(Polynomial* poly) {
      printf("Polynomial: ");
      Term* temp = poly->head;
      while (temp) {
         printf("%.2f*x^1 + ", temp->coefficient);
         temp = temp->next;
      }
      printf("\n");
   }

4. **多项式减法** (`subtractPolynomials`):
- 类似于加法，只是需要判断是相加还是相减。

   Polynomial* subtractPolynomials(Polynomial* p1, Polynomial* p2) {
      Polynomial* result = createPolynomial(0);
      Term* cur1 = p1->head;
      Term* cur2 = p2->head;
      while (cur1 && cur2) {
         if (cur1->coefficient > cur2->coefficient)
            result->head->coefficient = cur1->coefficient - cur2->coefficient, cur1++;
         else
            result->head->coefficient = cur2->coefficient - cur1->coefficient, cur2++;
      }
      while (cur1) {
         result->head->coefficient -= cur1->coefficient;
         cur1++;
      }
      while (cur2) {
         result->head->coefficient -= cur2->coefficient;
         cur2++;
      }
      result->degree = MAX(p1->degree, p2->degree);
      return result;
   }

请注意，这个实现假定`Term`结构体有一个`next`指针来连接下一个项。上述函数可能会导致内存泄漏，如果在不再需要链表时忘记释放内存，建议在实际项目中适当优化。以下是完整的示例：

//... 其他必要的库函数声明 ...

int main() {
    Polynomial* poly1 = createPolynomial(5);
    Polynomial* poly2 = createPolynomial(3);
    Polynomial* sum = addPolynomials(poly1, poly2);
    Polynomial* diff = subtractPolynomials(poly1, poly2);

    displayPolynomial(poly1);
    displayPolynomial(poly2);
    displayPolynomial(sum);
    displayPolynomial(diff);

    freePolyList(&poly1);
    freePolyList(&poly2);
    freePolyList(&sum);
    freePolyList(&diff);
    return 0;
}

void freePolyList(Polynomial** poly) {
    if (*poly != NULL) {
        Term* temp = (*poly)->head;
        while (temp != NULL) {
            Term* next = temp->next;
            free(temp);
            temp = next;
        }
        free(*poly);
        *poly = NULL;
    }
}