关于指针 l3 = l1; l1 = l1->next的问题

本文探讨了指针c如何指向指针a,当a的地址改变时c的行为,以及变量值改变对指针的影响实例。重点在于解释c=a与c指向a地址的区别,以及变量地址稳定性对指针操作的影响。

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#include<stdio.h>
#include<string.h>

int main(void)
{
	int b =3; int d =0; int *a = &b;int *c = NULL;
	c = a;
	printf("\na的地址是%p\n", a);
	printf("\nc的地址是%p\n", c);
	a = &d;
	printf("\na的地址是%p\n", a);
	printf("\nc的地址是%p\n", c);
	printf("%d", *c);
	b = 4;
	printf("\na的地址是%p\n", a);
	printf("\nc的地址是%p\n", c);
	printf("%d", *c);

// 指针c指向指针a的地址,

// a = &d;
// printf(“a是%d”, *a);
// printf("\n%d", *c);
// l3 = l1;
// l1 = l1->next;
}

a的地址改变与否并不影响c的地址改变(此时指针c指向指针a指向的地址),c = a;
仅仅代表c指向a的地址,并非c指向a,如果int变量b的值改变,3改成4,b的地址不会
改变,此时a指向b,c指向的也是b的地址,b改变之后, *a =4, *c 也等于4。
若a = &d, 此时a指向了一个新的地址,*a=0, 由于b指向的依旧是之前a指向的地址,
即int变量b的地址,此时*b = 3。
void InitPolylist(Polylist *L) {*L = (Polylist)malloc(sizeof(Polylist)); (*L)->next = NULL; } Polylist CreatePolylist()/*输入多项式的系数和指数,用尾插法建立一元多项式的链表*/ {Polylist L; Polynode *s; InitPolylist(&L); double coef; int exp; Polynode *r = L; scanf("%lf %d",&coef,&exp); while(coef != 0) { s = (Polynode *)malloc(sizeof(Polynode)); s->coef = coef; s->exp = exp; s->next = NULL; r->next = s; r = s; scanf("%lf %d",&coef,&exp); } r->next = NULL; return L; } int LengthPolylist(Polylist L) {Polylist r = L; int n = 0; while(r->next != NULL) { n++; r = r->next; } return n; } void OutputPolylist(Polylist L) { Polylist r = L->next; printf("inlcude %d coef/exp list is:\n",LengthPolylist(L)); while(r != NULL) { printf("%.2f,%d\n",r->coef,r->exp); r = r->next; } } Polylist AddPolylist()/*创建两个多项式并相加,完成后显示序列*/ {Polylist l1 = CreatePolylist(); Polylist l2 = CreatePolylist(); Polylist l3; InitPolylist(&l3); Polynode *s; Polylist r1 = l1->next, r2 = l2->next, r3 = l3; double sum; while(r1 != NULL && r2 != NULL) { s = (Polynode *)malloc(sizeof(Polynode)); if(r1->exp < r2->exp) { s->coef = r1->coef; s->exp = r1->exp; r3->next = s; r3 = s; r1 = r1->next; } else if (r1->exp == r2->exp) { sum = r1->coef + r2->coef; if(sum != 0) { s->coef = sum; s->exp = r1->exp; r3->next = s; r3 = s; r1 = r1->next; r2 = r2->next; } else { return l3; } } else { s->coef = r2->coef; s->exp = r2->exp; r3->next = s; r3 = s; r2 = r2->next; } } if(r1 != NULL){ r3->next = r1; } else { r3->next = r2; } return l3; } void ComputePolylist(Polylist L)/*计算多项式在x=%d的值*/ {Polylist r = L->next; double x = 0; double result = 0; scanf("%lf",&x); while(r != NULL) { result += r->coef * pow(x, r->exp); r = r->next; } printf("ComputePolylist in x=%.2f result is:%.2f\n",x,result); } void DestroyPolylist(Polylist L) { Polynode *p = L ,*q = L->next; while(q) { free(p); p = q; q = q->next; } free(p); printf("destroy"); } 解释一下这个代码
06-10
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