4-19

code/practise/17 指针的高级应用/01 显示一个月的提醒列表/readme.md

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+  #### 程序：显示一个月的提醒列表
+
+前面我们把字符串存储在二维数组中，但是这可能会浪费空间。后面的教学中我们设想使用指针数组存储字符串，让一维数组的每个元素都指向一个字符串字面量。如果数组元素是指向动态分配的字符串的指针，那么是可以实现我们的设想的。
+
+下面的程序对之前的程序作了小部分修改，修改的地方后面用注释注明了。

code/practise/17 指针的高级应用/01 显示一个月的提醒列表/reminder.c

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+#include<stdio.h>
+#include<string.h>
+#include<stdlib.h>
+
+#define MAX_REMIND 50
+#define MSG_LEN 100
+
+
+int read_line(char str[], int read_num);
+
+int main(void) {
+	
+	char* reminders[MAX_REMIND]; // 存放提示的数组 // change
+	char day_str[3];//当前日期转换为字符串
+	char msg_str[MSG_LEN + 1]; //当前输入的提示消息
+	int day, num_remind = 0; // 日期和当前提示数
+	int i, j;
+
+
+	for (;;) {
+
+		if (num_remind == MAX_REMIND) {
+			printf("-- No space left --\n");
+			break;
+		}
+
+		printf("Enter day and reminder:");
+
+		scanf("%2d", &day); //每月的日期只用两个数表示即可，只读 2 个字段
+
+		if (day == 0)
+			break;
+
+		sprintf(day_str, "%2d", day); // 将 day 以 "%2d" 的格式写入 day_str 字符数组中。"%2d" 保证小于10的天占两位右对齐
+		read_line(msg_str, MSG_LEN);
+		
+
+		// 寻找当前输入的提示应该放到提示数组的那个位置
+		for (i = 0; i < num_remind; i++) {
+			// 说明当前输入的日期应该排在此行前
+			if (strcmp(day_str, reminders[i]) < 0)
+				break;
+		}
+		
+		// 将当前输入的提示插入到正确的位置
+		for (j = num_remind; j > i; j--) {
+			reminders[j] = reminders[j - 1]; // change
+		}
+
+		reminders[i] = (char*)malloc(sizeof(msg_str) + sizeof(day_str) + 1); // change
+		
+		// change																	 
+		if (reminders[i] == NULL) {
+			printf("-- No space left --\n");
+			break;
+		}
+	
+		strcpy(reminders[i], day_str);
+		strcat(reminders[i], msg_str);// 刚好将 day_str 复制进去的空字符覆盖掉了
+
+		num_remind++;
+	}
+
+	printf("Day Reminder: \n");
+	for (i = 0; i < num_remind; i++)
+		printf("%s\n", reminders[i]);
+
+
+	return 0;
+}
+
+
+int read_line(char str[], int read_num) {
+
+	int ch, count = 0;
+
+	while ((ch = getchar()) != '\n') {
+		if (count < read_num) {
+			str[count++] = ch;
+		}
+	}
+
+	str[count] = '\0';
+
+	return count;
+}

code/practise/17 指针的高级应用/02 维护零件数据库（链表）/inventory2.c

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+#include<stdio.h>
+#include<stdlib.h>
+#include"readline.h"
+
+#define NAME_LEN 20
+
+typedef struct part {
+	int number;
+	char name[NAME_LEN + 1];
+	int on_hand;
+	struct part* next;
+}part;
+
+
+void menu();
+part* find_part(part* head, int number);
+void insert(part* head);
+void search(part* head);
+void update(part* head);
+void print(part* head);
+
+
+int main(void) {
+
+	char code = 'a';
+	part* head = (part*)malloc(sizeof(part));
+	head->next = NULL;
+
+	if (head == NULL) {
+		printf("Database establish failed\n");
+		exit(EXIT_SUCCESS);
+	}
+
+	menu();
+
+	for (;;) {
+		printf("Enter operation code: ");
+		scanf(" %c", &code);
+		while (getchar() != '\n') // skips to end of line
+			;
+		switch (code) {
+		case 'i': insert(head); break;
+		case 's': search(head); break;
+		case 'u': update(head); break;
+		case 'p': print(head); break;
+		case 'q': return 0;
+		default: printf("Illegal code.\n"); break;
+		}
+	}
+
+
+
+
+	return 0;
+}
+
+void menu() {
+
+	printf("                        ==================================\n");
+	printf("                        *                                *\n");
+	printf("                        *            i:  insert          *\n");
+	printf("                        *            s:  search          *\n");
+	printf("                        *            u:  undate          *\n");
+	printf("                        *            p:  print           *\n");
+	printf("                        *            q:  quit            *\n");
+	printf("                        *                                *\n");
+	printf("                        ==================================\n");
+}
+
+
+/**********************************************************
+*
+*	find_part: Looks up a part number in the inventory
+*			   array.Returns the array index if the part
+*			   number is found;otherwise,return -1
+*
+***********************************************************/
+part* find_part(part* head, int number) {
+
+	part* cur;
+
+	// 链表是按照编号升序排序的
+	for (cur = head->next; cur != NULL && cur->number > number;
+		cur = cur->next)
+		;
+	
+	if (cur == NULL)
+		return NULL;
+
+	if (cur->number == number)
+		return cur;
+
+}
+
+
+/**********************************************************
+*
+*	insert: Inserts the part into the database.Prints
+*		    an error message and returns prematurely
+*			if the part already exists or the database
+*			is full.
+*
+***********************************************************/
+void insert(part* head) {
+
+	int part_number;
+	part* cur, * prev, *new_part;
+	
+
+	printf("Enter part number: ");
+	scanf("%d", &part_number);
+	
+	// 寻找 part_number 所应插入的位置，我们需要 cur 遍历链表，但是应该保留 cur 前面的结点 prev 
+	// 退出循环条件：cur == NULL 说明是头插或尾插
+	//				 cur->number > part_number 说明 输入的编号重复
+	//												应该在 cur 和 prev 之间插入新的零件 或 头插
+	for (cur = head->next, prev = NULL;cur != NULL && cur->number < part_number ;
+		prev = cur, cur = cur->next)
+		;
+	
+	// 判断输入的编号是否于数据库中的现有重复
+	if (cur != NULL && cur->number == part_number) {
+		printf("Part already exists.\n");
+		return;
+	}
+
+	// 申请新结点
+	new_part = (part*)malloc(sizeof(part));
+
+	// 判断申请是否成功
+	if (new_part == NULL) {
+		printf("Database is full; can't add more parts.\n");
+		return;
+	}
+
+	
+	new_part->number = part_number;
+	printf("Enter part name: ");
+	read_line(new_part->name, NAME_LEN);
+	printf("Enter quantity on hand: ");
+	scanf("%d", &new_part->on_hand);
+	
+	// 插入的方式：
+	// 链表为空时：对 head 进行操作（prev == NULL, cur == NULL）
+	// 链表不为空：
+	//			  头插：对 head 操作 (prev == NULL, cur != NULL)
+	//			  尾插：对 prev 操作 (prev != NULL, cur == NULL)
+	//			  普通位置插入：对 prev 操作(prev,cur 都不为 NULL)
+	new_part->next = cur;
+
+	if (prev == NULL)
+		head->next = new_part;
+	else
+		prev->next = new_part;
+
+}
+
+
+/************************************************************
+*
+*	search: Look up a part by the number user enters.
+*			If the part exists, prints the name and quantity
+*			on hand;if not, print an error message.
+*
+************************************************************/
+void search(part* head) {
+
+	int number;
+	part* trg;
+
+	printf("Enter part number: ");
+	scanf("%d", &number);
+
+	trg = find_part(head, number);
+
+	if (trg == NULL) {
+		printf("Part not found.\n");
+		return;
+	}
+
+	printf("Part name: %s\n", trg->name);
+	printf("Quantity on hand: %d\n", trg->on_hand);
+
+}
+
+
+/************************************************************
+*
+*	update: Prompts user to enter a number.
+*			Print an error message if the part doesn't exist;
+*			otherwise,prompts the user to enter change in
+*			quantity on hand and updates the database.
+*
+************************************************************/
+
+void update(part* head) {
+
+	int number, change;
+	part* trg;
+
+	printf("Enter part number: ");
+	scanf("%d", &number);
+
+	trg = find_part(head, number);
+
+	if (trg == NULL) {
+		printf("Part not found.\n");
+		return;
+	}
+
+	printf("Enter change in quantity on hand(- means minus): ");
+	scanf("%d", &change);
+	trg->on_hand += change;
+
+}
+
+
+/************************************************************
+*
+*	print: Print a listing of all parts in the database,
+*		   showing the part number,part name and quantity
+*		   on hand.Parts are printed in the order in which
+*		   they were entered into the database.
+*
+************************************************************/
+
+void print(part* head) {
+
+
+	printf("Part Number      Part Name      Quantity on Hand\n");
+	for (part* cur = head->next; cur != NULL; cur = cur->next) {
+		printf("%6d%20s%15d\n", cur->number, cur->name, cur->on_hand);
+	}
+}