C程序设计 （第四版） 谭浩强 习题9.7

习题 9.7 在第9章例9.9和例9.10的基础上，写一个函数del，用来删除动态链表中指定的结点。

IDE工具：VS2010

Note: 使用不同的IDE工具可能有部分差异。

代码块:

由于链表是动态链表，不能按照结构体变量为数组的时候通过指针增减调整指针指向，借鉴网上的提示，将原来的单链表增加一个结构体内指针，成为双向链表。

方法1：在原例题的基础上增加

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

struct Student{
    
	int num;
	float score;
	Student *prev;                      //此处为增加的指向上一个结构体变量的指针
	Student *next;
};

Student *input();                       //定义输入函数
void print(Student *stu);               //定义输出函数
Student *del(Student *stu, float n);    //定义删除函数

int main(){
    
	Student *stud;                      //定义结构体变量并输入动态链表
	stud = input();
	print(del(stud, 99));               //调用输出函数，参数为删除函数返回的指针值
	
	system("pause");
	return 0;
}

//输入函数
Student *input(){
    
	Student *p1, *p2, *head;
	int n = 0;
	p1 = p2 = (Student*)malloc(sizeof(Student));
	printf("Please enter No.%d student info: ", n+1);
	scanf("%d %f", &p1->num, &p1->score);
	head = NULL;
	while(p1->num != 0){
    
		n++;
		if(n == 1){
    
			head = p1;
			p1->prev = NULL;                     //在原例题基础上，将上一个指针指向上一个结构体指针
		}
		else{
    
			p2->next = p1;
			p1->prev = p2;
		}
		p2 = p1;
		p1 = (Student*)malloc(sizeof(Student));
		printf("Please enter No.%d student info: ", n+1);
		scanf("%d %f", &p1->num, &p1->score);
	}
	p2->next = NULL;
	return head;
}

//输出函数
void print(Student *stu){
    
	Student *p;
	for(p = stu; p != NULL; p = p->next)
		printf("%d %.2f\n", p->num, p->score);
}

//删除函数
Student *del(Student *stu, float n){
    
	Student *p, *head;
	for(p = stu, head = p; p != NULL; p = p->next)
		if(p->score == n){
    
			if(head == p){
    
				head = p->next;
			}
			else if(p->next == NULL){
    
				p->prev->next = NULL;
			}
			else{
    
				p->prev->next=p->next;
			}
		}
	return head;
}

方法2：使用指针，自定义类型，结构体，动态分配内存，函数返回类型调整为空。

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

typedef struct Student{
    
	int num;
	float score;
	Student *prev;
	Student *next;
}Student;

//初始化学生并输入学生人数
void initialStu(Student **stu){
    
	int *n = (int*)malloc(sizeof(int));

	//输入要建立的学生人数
	printf("Enter the number of students: ");
	scanf("%d", n);
	while(*n <= 0){
    
		printf("Number can't less or equal than 0!\nEnter the number of students: ");
		scanf("%d", n);
	}

	printf("\n");

	//创建头结点，头结点的num指定为学生总人数
	Student *head = (Student*)malloc(sizeof(Student));
	head->num = *n;
	head->next = NULL;
	*stu = head;
	
	n = NULL;
	free(n);
}

//判断学生编号是否重复
int isRepeat(Student *stu, int num){
    
	for(Student *p = stu->next; p != NULL; p = p->next){
    
		if(p->num == num){
    
			return 1;
		}
	}
	return 0;
}

void creatStu(Student *stu){
    
	Student *head = stu;
	Student *p1 = head;
	Student *p2 = head;
	
	printf("Enter %d students info:\n\n", head->num);

	for(int i = 0; i < head->num; i++){
    
		p1 = (Student*)malloc(sizeof(Student));
		p1->next = NULL;
		p1->prev = p2;

		printf("Enter No.%d student number(100 ~ 999): ", i + 1);
		scanf("%d", &p1->num);
		while(p1->num < 100 || p1->num > 999 || isRepeat(stu, p1->num) == 1){
    
			if(isRepeat(stu, p1->num) == 1){
    
				printf("Number Repeat! ");
			}
			else{
    
				printf("Number Error! ");
			}
			printf("Retry!\nEnter No.%d student number(100 ~ 999): ", i + 1);
			scanf("%d", &p1->num);
		}
		
		printf("Enter No.%d student score(0 ~ 100): ", i + 1);
		scanf("%f", &p1->score);
		while(p1->score < 0 || p1->score > 100){
    
			printf("Score Error! Retry!\nEnter No.%d student score(0 ~ 100): ", i + 1);
			scanf("%f", &p1->score);
		}
		
		p2->next = p1;
		p1 = p1->next;
		p2 = p2->next;
		
		printf("\n");
	}
}

void printStu(Student *stu){
    
	printf("\nThe info of %d students:\n", stu->num);
	
	for(Student *p = stu->next; p != NULL; p = p->next){
    
		printf("Number: %-4d  Score: %-6.2f\n", p->num, p->score);
	}
	
	printf("\n");
}

void delStu(Student *stu){
    
	int *delNum = (int*)malloc(sizeof(int));
	
	printf("Enter the student number you want to delete: ");
	scanf("%d", delNum);
	
	int sign = 0;
	for(Student *p = stu->next; p != NULL; p = p->next){
    
		if(p->num == *delNum){
    
			sign = 1;
			printf("\nThe student info:\n");
			printf("Number: %-4d  Score: %-6.2f\n\n", p->num, p->score);
			p->next->prev = p->prev;
			p->prev->next = p->next;
			p = NULL;
			free(p);
			break;
		}
	}
	if(sign == 0){
    
		printf("None!\n\n");
	}

	free(delNum);
}

int main(){
    
	Student *stu = NULL;

	initialStu(&stu);

	creatStu(stu);
	printStu(stu);
	
	delStu(stu);
	printStu(stu);
	
	free(stu);
	
	system("pause");
	return 0;
}