From fc1df13600983f5e5b446b5509805022dfb80092 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?=E7=94=98=E5=B0=8Fqiang?= <3249994165@qq.com>
Date: Wed, 21 Dec 2022 20:43:49 +0800
Subject: [PATCH] =?UTF-8?q?=E6=88=91=E7=9A=84=E7=AC=AC=E5=A4=9A=E5=B0=91?=
 =?UTF-8?q?=E6=AC=A1=E4=BD=9C=E4=B8=9A=EF=BC=9F?=
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Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

---
 .../12.19.md"                                 |  67 +++++++-----
 .../12.21.md"                                 | 103 ++++++++++++++++++
 2 files changed, 144 insertions(+), 26 deletions(-)
 create mode 100644 "\347\254\224\350\256\260&\344\275\234\344\270\232/12.21.md"

diff --git "a/\347\254\224\350\256\260&\344\275\234\344\270\232/12.19.md" "b/\347\254\224\350\256\260&\344\275\234\344\270\232/12.19.md"
index 523af9d..43104f7 100644
--- "a/\347\254\224\350\256\260&\344\275\234\344\270\232/12.19.md"
+++ "b/\347\254\224\350\256\260&\344\275\234\344\270\232/12.19.md"
@@ -60,10 +60,8 @@ public class H13 {
 
 ```java
 package 循环;
-
 import java.util.Arrays;
 import java.util.Scanner;
-
 public class H14 {
 //    在主函数中接收10个数存入数组，在自定义函数中，将该数组中的最大值与第一个元素交换，最小值与最后一个元素交换，然后在主函数中输出交换后的数组
 public static void main(String[] args) {
@@ -76,33 +74,50 @@ public static void main(String[] args) {
                 arr[i]=shuru ;
         }
         System.out.println(Arrays.toString(arr));
-        int max  =arr[0];
-        int min  =arr[0];
-        maxx (max,arr);
-        System.out.println("最大值:"+maxx( max,arr));
-        minn(min,arr);
-        System.out.println("最小值:"+minn(min,arr));
-        int t=0;
-
-
-}
-        static int maxx (int max,int [] arr){
-        for (int i=0;i<arr.length;i++){
-                if (max<i){
-                        max=i;int t=max;max=arr[t];
-                }
-        }
-                return max;
-        }
-        static int minn (int min,int [] arr){
-                for (int i=0;i<arr.length;i++){
-                        if (min==i){
-                                min=i;
+        changeArray(arr);
+        System.out.println(Arrays.toString(arr));
+}static void  changeArray(int []arr){
+        int max=arr[0],maxindex =0;
+        int min=arr[0],minindex =0;
+                for (int i = 0; i <arr.length ; i++) {
+                        if (arr[i]>max){
+                                max=arr[i];
+                                maxindex=i;
+                        }
+                        if (arr[i]<min){
+                                min=arr[i];
+                                minindex=i;
                         }
                 }
-                return min;
+                int tmp =arr[0];
+                arr[0]=max;
+                arr[maxindex]=tmp;
+                int tnp=arr[0];
+                tnp=arr[arr.length-1];
+                arr[arr.length-1]=min;
+                arr[minindex]=tnp;
         }
-
         }
+
+```
+
+```java
+package 循环;
+
+public class H16 {
+    public static void main(String[] args) {
+        int [] num={10,23,56,8,9,4,6,34,678,7,5};
+         int sum=   he(num);
+        System.out.println(sum);
+    }
+    static int he (int [] num){
+        int count=0;
+        for (int a:num
+             ) {
+            count+=a;
+        }return count;
+    }
+}
+
 ```
 
diff --git "a/\347\254\224\350\256\260&\344\275\234\344\270\232/12.21.md" "b/\347\254\224\350\256\260&\344\275\234\344\270\232/12.21.md"
new file mode 100644
index 0000000..8390d3a
--- /dev/null
+++ "b/\347\254\224\350\256\260&\344\275\234\344\270\232/12.21.md"
@@ -0,0 +1,103 @@
+# 学生管理系统
+
+```java
+package 循环;
+
+import java.util.Scanner;
+
+public class H17 {
+//    把扫描器放在最外层，让所有方法都可以用
+    static Scanner sc =new Scanner(System.in);
+    public static void main(String[] args) {
+        String [] students =new String[10];
+        students[0]="苏清华";
+        students[1]="林佳泽";
+        while (true){
+            start();
+        choicMenu(sc.nextInt(),students ,sc);
+        }
+    }public static  void start (){
+        System.out.println("-----------------------------"+
+                "\n- 欢迎使用三班的学生管理系统-"+
+                "\n- \t\t1.浏览所有学生信息\t\t-"+
+                "\n- \t\t2.添加学生信息\t\t-"+
+                "\n- \t\t3.修改学生信息\t\t-"+
+                "\n- \t\t4.删除学生信息\t\t-"+
+                "\n- \t\t5.查询学生信息\t\t-"+
+                "\n- \t\t6.退出管理系统\t\t-"+
+                "\n------------------------------");
+    }
+    public static void choicMenu(int num,String[]stu,Scanner sc){
+        switch (num){
+            case 1:
+//                System.out.println("你选择了浏览学生信息");
+                viewAllStuendt(stu);
+                break;
+            case 2:
+                addStudent(stu);
+//                System.out.println("你选择了添加学生信息");
+                break;
+            case 3:
+                System.out.println("你选择了修改学生信息");
+                break;
+            case 4:
+                System.out.println("你选择了删除学生信息");
+                break;
+            case 5:
+                System.out.println("你选择了查询学生信息");
+
+                break;
+            case 6:
+                System.out.println("你选择了退出管理系统");
+                break;
+            default:
+                System.out.println("选项错误");
+        }
+    }
+    public static void viewAllStuendt(String[]stu){
+        System.out.println("三班现有以下学生:");
+        for (String name:stu){
+            if (name==null){
+                continue;
+            }
+            System.out.print(name+"\t");
+        }
+    }
+    public static void addStudent(String[]stu){
+       System.out.println("请输入你要添加的学生：");
+       String name =sc.next();
+       int index =searchIndex(stu,name);
+       if (index !=-1){
+           System.out.println("该学生已存在，请不要重复添加");
+       }else{
+           int nullIndex =searchIndex(stu,null);
+           stu[nullIndex] =name;
+           System.out.println("添加成功");
+           viewAllStuendt(stu);
+       }
+    }
+    //4.1
+    public static int searchIndex(String[] stu,String str){
+        int index =-1;
+        if (str==null){
+            for (int i=0;i<stu.length;i++){
+                if(stu[i]==null){
+                     index=i;
+                     break;
+                }
+            }
+        }
+        else{
+            for (int i=0;i< stu.length;i++){
+            if (str.equals(stu[i])){
+                 index=i;
+                 return index;
+            }
+        }
+        }
+        return index;
+    }
+}
+
+```
+
-- 
Gitee