switch语句那里为什么编译显示“program received signal SIDSEGV”?

//一元多项式加减计算器
#include<stdio.h>
#include<stdlib.h>
typedef struct node{
    int coef;
    int expen;
    struct node *next;
}List;
int Compare_Polyn( int a, int b )
{
    if( a > b ){
        return 1;
    }
    if( a = b ){
        return 0;
    }
    if( a < b ){
        return -1;
    }
}
List *Create_Polyn( List* current, int a, int b )
{
    List *p = (List *)malloc(sizeof(List)); 
    p->coef = a;
    p->expen = b;
    if( current != NULL ){
        current->next = p;
        current = current->next;
        current->next = NULL;
        return current;
    }
    else{
        printf("ERROR: the current pointer is NULL!\n");
        return current;
    }
}
void Add_Polyn( List * p1, List *p2 , List * head3 )
{
    if( p1==NULL || p2==NULL ){
        printf("ERROR: Add_Polyn is wrong!\n");
    }
    List *p3;
    p3 = head3;
    while( p1 && p2 ){
        switch( Compare_Polyn( p1->expen, p2->expen ) ){
            case 1 : 
                Create_Polyn( p3, p2->coef, p2->expen ); p2++; break;
            case 0 :
                Create_Polyn( p3, (p1->coef + p2->coef), ( p1->expen ) ); p1++; p2++; break;
            case -1 :
                Create_Polyn( p3, p1->coef, p1->expen);p1++; break;
            default :
                printf("ERROR: switch and compare is wrong!\n"); break;    
        }
    }
    while( p1 ){
        p3 = Create_Polyn( p3, p1->coef, p1->expen );
        p1++;
    }    
    while( p2 ){
        p3 = Create_Polyn( p3, p2->coef, p2->expen );
        p2++;
    }
}
void Print_Polyn( List * head3 )
{
    while( head3 != NULL ){
        printf("%d %d\n", head3->coef, head3->expen );
    }
}
int main()
{
    int a, b;
    List * head1, *p1;
    head1 = (List *)malloc( sizeof( List) );
    p1 = head1;
    p1->next = NULL;
    printf("请按照规范输入第一个一元多项式(以系数和指数都为0时结束)：\n");
    scanf("%d %d", &a, &b);
    
    //生成存放第一个一元多项式的链表 
    while( b ){
        p1 = Create_Polyn( p1, a, b );
        scanf("%d %d", &a, &b);    
    }
    p1->next = NULL;
    p1 = head1->next;
    
    int c, d;
    List * head2, *p2;
    head2 = (List *)malloc( sizeof( List) );
    p2 = head2;
    printf("请按照规范输入第二个一元多项式(以系数和指数都为0时结束)：\n");
    scanf("%d %d", &c, &d);
    
    //生成存放第二个一元多项式的链表 
    while( d ){
        p2 = Create_Polyn( p2, c, d );
        scanf("%d %d", &c, &d);    
    }
    p2->next = NULL;
    p2 = head2->next;    
    
    //第三个链表用来存放结果 
    List *head3;
    head3 = (List *)malloc( sizeof( List) );
    head3->next = NULL;
    Add_Polyn( p1, p2, head3);

    //开始打印
    Print_Polyn( head3 );
    
    return 0;         
 }

刚学数据结构不久，还望各位帮帮我这只小菜鸡。

可以提供截图看看吗？