C 链表实现多项式

原来文章是用于转载，随笔才是原创，好吧，那发过来吧。

第一篇文章，如题用链表实现了多项式，包括输入、输出和三种运算。

这次代码主要遇到两个问题：scanf的连续调用，以及一个神奇的很不科学的bug——i的初始化问题

代码贴下来如下：

//本程序使用C语言创建一个链表来表示多项式
//多项式按照升序进行排列
//实现多项式的加、减、乘三个运算
#include<stdlib.h>
#include<stdio.h>
#define new(type) (type*)malloc(sizeof(type))
typedef struct _Term Term;
struct _Term{
    float coef;    //系数
    int exp;       //指数
    Term *next;
};
Term* plus (Term* head1,Term* head2);
Term* minus(Term* head1,Term* head2);
Term* multi(Term* head1,Term* head2);
void print(Term* head);
void scan(Term* head);
int main(){
    Term *head1 = new(Term);
    head1->next = NULL;
    Term *head2 = new(Term);
    head2->next = NULL;
    printf("Input format: coef,exp\n");
    printf("Enter the ### to end the input.\n");
    printf("Input Polynomal 1:\n");
    scan(head1);
    printf("Input Polynomal 2:\n");
    scan(head2);
    Term * result1 = new(Term);
    Term * result2 = new(Term);
    Term * result3 = new(Term);
    result1 = plus(head1,head2);
    result2 = minus(head1,head2);
    result3 = multi(head1,head2);
    printf("result of plus:");
    print(result1);
    printf("result of minus:");
    print(result2);
    printf("result of multi:");
    print(result3);
    return 0;
}
void print(Term *head){
    Term *temp = head->next;
    while(temp != NULL){
        if(temp->coef > 0)
            printf("+%gx^%d",temp->coef,temp->exp);
        else if(temp->coef < 0)
            printf("%gx^%d",temp->coef,temp->exp);
        temp = temp->next;
    }
    printf("\n");
}
void scan(Term *head){
    float coef;
    int exp;
    while(scanf("%f,%d",&coef,&exp) == 2){
        Term *ptr = new(Term);
        ptr->exp = exp;
        ptr->coef = coef;
        if(head->next == NULL){
            ptr->next = NULL;
            head->next = ptr;
        }
        else{
            Term* temp = head->next;
            Term* temp2 = head;
            while(temp != NULL && temp->exp > ptr->exp){
                temp = temp->next;
                temp2 = temp2->next;
            }
            if(temp == NULL){
                ptr->next = NULL;
                temp2->next = ptr;
            }
            else{
                ptr->next = temp2->next;
                temp2->next = ptr;
            }
        }
    }
    while(getchar() != '\n');
    return;
}
Term* plus(Term* head1,Term* head2){
    Term *newhead = new(Term);
    newhead->next = NULL;
    Term *temp1 = head1->next;
    Term *temp2 = head2->next;
    Term *temp = newhead;
    while(temp1 != NULL && temp2 != NULL){
        Term *ptr = new(Term);
        if(temp1->exp < temp2->exp){
            ptr->next = NULL;
            ptr->coef = temp2->coef;
            ptr->exp = temp2->exp;
            temp->next = ptr;
            temp2 = temp2->next;
        }
        else if(temp1->exp > temp2->exp){
            ptr->next = NULL;
            ptr->coef = temp1->coef;
            ptr->exp = temp1->exp;
            temp->next = ptr;
            temp1 = temp1->next;
        }
        else{
            ptr->next = NULL;
            ptr->coef = temp1->coef + temp2->coef;
            ptr->exp = temp1->exp;
            temp->next = ptr;
            temp1 = temp1->next;
            temp2 = temp2->next;
        }
        temp = temp->next;
    }
    if(temp1 == NULL){
        while(temp2 != NULL){
            Term *ptr = new(Term);
            ptr->next = NULL;
            ptr->coef = temp2->coef;
            ptr->exp = temp2->exp;
            temp->next = ptr;
            temp2 = temp2->next;
            temp = temp->next;
        }
    }
    else if(temp2 == NULL){
        while(temp1 != NULL){
            Term *ptr = new(Term);
            ptr->next = NULL;
            ptr->coef = temp1->coef;
            ptr->exp = temp1->exp;
            temp->next = ptr;
            temp1 = temp1->next;
            temp = temp->next;
        }
    }
    return newhead;
}
Term* minus(Term* head1,Term* head2){
    Term *newhead = new(Term);
    newhead->next = NULL;
    Term *temp = newhead;
    Term *temp2 = head2->next;
    while(temp2 != NULL){
        Term *ptr = new(Term);
        ptr->next = NULL;
        ptr->coef = -temp2->coef;
        ptr->exp = temp2->exp;
        temp->next = ptr;
        temp2 = temp2->next;
        temp = temp->next;
    }
    newhead =  plus(head1,newhead);
    return newhead;
}
Term* multi(Term* head1,Term* head2){
    int maxExp,i;
    Term *newhead = new(Term);
    newhead->next = NULL;
    Term *temp = newhead;
    Term *temp1 = head1->next;
    Term *temp2 = head2->next;
    if(temp1 != NULL && temp2 != NULL)
        maxExp = temp1->exp + temp2->exp;
    printf("maxExp:%d\n",maxExp);
    float *result = malloc(sizeof(float) * (maxExp+1));
    i = 0;
    while(i <= maxExp){
        result[i] = 0.0;
        i ++;
    }
    while(temp1 != NULL){
        temp2 = head2->next;
        while(temp2 != NULL){
            i = temp1->exp + temp2->exp;
            printf("exp:%d,%d\n",temp1->exp,temp2->exp);
            printf("coef:%f,%f\n",temp1->coef,temp2->coef);
            printf("result:%f",result[i]);
            result[i] = result[i] + temp1->coef * temp2->coef;
            printf("result[%d]=%f\n",i,result[i]);
            temp2 = temp2->next;
        }
        temp1 = temp1->next;
    }
   for(i = maxExp; i >= 0; i --){
        if(result[i] != 0){
            Term *ptr = new(Term);
            ptr->next = NULL;
            ptr->coef = result[i];
            ptr->exp = i;
            temp->next = ptr;
            temp = temp->next;
        }
    }
    free(result);
    return newhead;
}

先说第一个问题，在连续两次使用scanf的时候，发现总是第二个scanf不能获取输入。

查阅网上相关资料后明白了其中的原理，现在举例如下：

第一次使用scanf("%d\n",&i);

你会有类似这样的输入：1\n，这里问题的关键就在于第二个字符，回车，他还留在缓存区的，

这样当你第二次调用scanf()的时候，他会先读取回车自然就不能继续输入了，

解决这个问题只需要添加一句getchar()，将其从缓存区取出，就能解决了。

第二个不科学的bug，我至今也没有想明白，就是在169行，最开始我没有初始化i，那么在main函数中的调用肯定错误

但是当我在调用之前，加上一句printf("xxxx");后他就神奇的对了，至今不明白，希望懂的人赐教。