使用c语言的知识完成：一元多项式的单链表表示及其运算 （1）采用单链表存储结构，设计并实现一元多式项的表示及其创建、输出、相加、相减等操作。 （2）针对所选择的求解问题，编写测试程序，并选取适当的测试数据，通过运行结果验证算法和程序设计的正确性。

在C语言中，我们可以使用结构体和指针来表示一元多项式。首先，定义一个`Term`结构体，包含系数`coefficient`和指数`exponent`：

typedef struct Term {
    double coefficient;
    int exponent;
} Term;

// 创建一个新的term节点
Term* createTerm(double c, int e) {
    Term* newTerm = (Term*)malloc(sizeof(Term));
    if (newTerm != NULL) {
        newTerm->coefficient = c;
        newTerm->exponent = e;
    }
    return newTerm;
}

// 输出一个term
void printTerm(Term* t) {
    printf("Coefficient: %lf, Exponent: %d\n", t->coefficient, t->exponent);
}

// 单链表表示多项式
typedef struct Polynomial {
    Term* head;
    int size;
} Polynomial;

// 创建空多项式
Polynomial* createPolynomial() {
    Polynomial* poly = (Polynomial*)malloc(sizeof(Polynomial));
    poly->head = NULL;
    poly->size = 0;
    return poly;
}

// 添加term到多项式
void addTerm(Polynomial* poly, Term* term) {
    if (poly->head == NULL) {
        poly->head = term;
    } else {
        Term* current = poly->head;
        while (current->next != NULL && current->exponent < term->exponent) {
            current = current->next;
        }
        if (current->exponent > term->exponent) {
            term->next = current->next;
            current->next = term;
        } else {
            term->next = NULL;
            current->next = term;
        }
    }
    poly->size++;
}

接下来，我们实现多项式的加法和减法：

// 加法：两个多项式的和
Polynomial* addPolynomials(Polynomial* poly1, Polynomial* poly2) {
    Polynomial* result = createPolynomial();
    Term* current1 = poly1->head, *current2 = poly2->head;
    
    while (current1 != NULL || current2 != NULL) {
        if (current1 != NULL && (current2 == NULL || current1->exponent < current2->exponent)) {
            addTerm(result, current1);
            current1 = current1->next;
        } else if (current1 != NULL && current1->exponent > current2->exponent) {
            current2 = current2->next;
        } else {
            // 如果两个term的指数相等，则计算它们的系数之差作为新的term
            double diff_coeff = current1->coefficient - current2->coefficient;
            addTerm(result, createTerm(diff_coeff, current1->exponent));
            current1 = current1->next;
            current2 = current2->next;
        }
    }
    return result;
}

// 减法：第一个多项式减去第二个多项式
Polynomial* subtractPolynomials(Polynomial* poly1, Polynomial* poly2) {
    Polynomial* result = createPolynomial();
    Term* current1 = poly1->head, *current2 = poly2->head;
    
    while (current1 != NULL || current2 != NULL) {
        if (current1 != NULL && (current2 == NULL || current1->exponent < current2->exponent)) {
            addTerm(result, current1);
            current1 = current1->next;
        } else if (current1 != NULL && current1->exponent > current2->exponent) {
            current2 = current2->next;
        } else {
            // 如果两个term的指数相等，则计算它们的系数之差作为新的term
            double diff_coeff = current1->coefficient - current2->coefficient;
            if (diff_coeff >= 0) {
                addTerm(result, createTerm(diff_coeff, current1->exponent));
            }
            current1 = current1->next;
            current2 = current2->next;
        }
    }

    // 如果poly2有剩余未处理的term，需要添加负数版本
    if (current2 != NULL) {
        for (; current2 != NULL; current2 = current2->next) {
            addTerm(result, createTerm(-current2->coefficient, current2->exponent));
        }
    }
    return result;
}

最后，你可以编写测试函数来验证这些功能：

int main() {
    Polynomial* poly1 = createPolynomial();
    Polynomial* poly2 = createPolynomial();

    // 添加测试项...
    // 测试addTerm()
    // 测试printPolynomial()

    Polynomial* sum = addPolynomials(poly1, poly2);
    printPolynomial(sum);

    Polynomial* diff = subtractPolynomials(poly1, poly2);
    printPolynomial(diff);

    freePolygons(&poly1, &poly2, &sum, &diff); // 自定义的释放多项式链表的函数

    return 0;
}

注意，这只是一个简化的示例，实际项目中可能还需要考虑更全面的错误处理和边界条件检查。