请问各位大神！！！关于链表问题一元多项式方程相加程序运行时输出heada时是垃圾值

#include
#include
#include

typedef struct polynode
{
float coef;
int exp;
struct polynode *next;
}polynode,*PLinklist;

PLinklist Create(int n)
{
PLinklist L,p;
int i;

L = (PLinklist)malloc(sizeof(polynode));
L->next = NULL;

for(i=n; i>0 ;--i)
{
p = (PLinklist)malloc(sizeof(polynode));
scanf("%f%d",&p->coef,&p->exp);
p->next = L->next;
L->next = p;
}

return(L);
}

PLinklist Attach(float co,int ex,PLinklist o)
{
PLinklist c;
c = (PLinklist)malloc(sizeof(polynode));
c->coef = co;
c->exp = ex;
o->next = c;
return c;
}

void Print(PLinklist L)
{
int i = 0;
PLinklist p = L;

while(p->next != NULL)
{
i++;
printf("%fx^%d ",p->coef,p->exp);
p=p->next;
}

printf("\n");
}

PLinklist Add(PLinklist A,PLinklist B)
{
PLinklist C;
PLinklist o;
PLinklist p = A;
PLinklist q = B;

float sum;

C = (PLinklist)malloc(sizeof(polynode));

o=C;

while((p != NULL) && (q != NULL))
{
if(p->exp == q->exp)
{
sum = p->coef+q->coef;
if(sum != 0)
o = Attach(sum,p->exp,o);
p = p->next;
q = q->next;
}

else if(p->exp < q->exp)
{
o = Attach(q->coef,q->exp,o);
q = q->next;
}
else{
o = Attach(p->coef,p->exp,o);
p = p->next;
}
}
while(p != NULL)
{
o = Attach(p->coef,p->exp,o);
p = p->next;
}
while(q != NULL)
{
o = Attach(q->coef,q->exp,o);
q = q->next;
}
o->next = NULL;
p = C;
C = C->next;
return C;
}

void main()
{
int n;
PLinklist A, B, C;
printf("Input the length of A :\n");
scanf("%d",&n);
A = Create(n);
Print(A);
printf("Input the length of B :\n");
scanf("%d",&n);
B = Create(n);
Print(B);
C = Add(A,B);
Print(C);
}

因为你的Create函数创建的链表是带头结点的（头结点中的coef,exp存的是随机值）
你Print函数应该从L->next开始进行循环，而且while判断的应该是p,而不是p->next
改成下面这样：

 #include <stdio.h>
#include <malloc.h>
#include <stdlib.h>

typedef struct polynode
{
    float coef;
    int exp;
    struct polynode *next;
}polynode, *PLinklist;

PLinklist Create(int n)
{
    PLinklist L, p;
    int i;

    L = (PLinklist)malloc(sizeof(polynode));
    L->next = NULL;

    for (i = n; i>0; --i)
    {
        p = (PLinklist)malloc(sizeof(polynode));
        scanf("%f%d", &p->coef, &p->exp);
        p->next = L->next;
        L->next = p;
    }

    return(L);
}

PLinklist Attach(float co, int ex, PLinklist o)
{
    PLinklist c;
    c = (PLinklist)malloc(sizeof(polynode));
    c->coef = co;
    c->exp = ex;
    o->next = c;
    return c;
}

void Print(PLinklist L)
{
    int i = 0;
    PLinklist p = L->next;

    while (p != NULL)
    {
        i++;
        printf("%fx^%d ", p->coef, p->exp);
        p = p->next;
    }

    printf("\n");
}

PLinklist Add(PLinklist A, PLinklist B)
{
    PLinklist C;
    PLinklist o;
    PLinklist p = A;
    PLinklist q = B;

    float sum;

    C = (PLinklist)malloc(sizeof(polynode));

    o = C;

    while ((p != NULL) && (q != NULL))
    {
        if (p->exp == q->exp)
        {
            sum = p->coef + q->coef;
            if (sum != 0)
                o = Attach(sum, p->exp, o);
            p = p->next;
            q = q->next;
        }

        else if (p->exp < q->exp)
        {
            o = Attach(q->coef, q->exp, o);
            q = q->next;
        }
        else{
            o = Attach(p->coef, p->exp, o);
            p = p->next;
        }
    }
    while (p != NULL)
    {
        o = Attach(p->coef, p->exp, o);
        p = p->next;
    }
    while (q != NULL)
    {
        o = Attach(q->coef, q->exp, o);
        q = q->next;
    }
    o->next = NULL;
    p = C;
    C = C->next;
    return C;
}

void main()
{
    int n;
    PLinklist A, B, C;
    printf("Input the length of A :\n");
    scanf("%d", &n);
    A = Create(n);
    Print(A);
    printf("Input the length of B :\n");
    scanf("%d", &n);
    B = Create(n);
    Print(B);
    C = Add(A, B);
    Print(C);
}