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+### 作业
+
+在主函数中产生20个0-10之间的随机数，将这20个随机数存入数组，并通过函数计算某个数在这些随机数中出现的次数（这“某个数”是在主函数中由用户输入的）
+
+```java
+import java.util.Random;
+import java.util.Scanner;
+
+public class zy18 {
+        public static void main(String[] args) {
+            int[] suiji =new int[20];
+            Random ra =new Random();
+            Scanner sc =new Scanner(System.in);
+            System.out.println("请输入你要查找个数的数字");
+            int chazhao=sc.nextInt();
+            for (int i=0;i<suiji.length;i++){
+                suiji[i]=ra.nextInt(11);
+                System.out.print(suiji[i]+" ");
+            }
+            cha(suiji,chazhao);
+        }
+        public static void cha(int[] shu,int zhao){
+            int count = 0;
+            for (int i=0;i<shu.length;i++){
+                if (shu[i]==zhao){
+                    count++;
+                }
+            }
+            System.out.println("\n"+count);
+        }
+    }
+```
+
+
+
+计算圆的面积和周长，在主函数中接受圆的半径，在自定义函数中计算并输出。
+
+```java
+import java.util.Scanner;
+
+public class zy19 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("输入圆的半径");
+        double r = sc.nextDouble();
+        count(r);
+    }
+    public static void count(double r) {
+        double c=2*3.14*r;
+        double s=3.14*(r*r);
+        System.out.println("圆的半径为："+r+"\n圆的周长为："+c+"\n圆的面积为："+s);
+    }
+}
+```
+
+
+
+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。
+
+```java
+import java.util.Scanner;
+
+public class zy20 {
+    public static void main(String[] args) {
+        Scanner sc =new Scanner(System.in);
+        System.out.println("输入十个数");
+        int[] shuzu = new int[10];
+        for(int i=0;i<shuzu.length;i++){
+            shuzu[i]= sc.nextInt();
+        }
+        for(int i=0;i<shuzu.length;i++){
+            System.out.print(shuzu[i]+" ");
+        }
+        System.out.println();
+        cha(shuzu);
+    }
+    public static void cha(int[] shu) {
+        int max=shu[0];
+        int maxshu=0;
+        int minshu=0;
+        for(int i=0;i<shu.length;i++){
+            if (max<shu[i]){
+                max=shu[i];
+                maxshu=i;
+            }
+        }
+        int zhuangzai=0;
+        zhuangzai=shu[0];
+        shu[0]=shu[maxshu];
+        shu[maxshu]=zhuangzai;
+        int min=shu[0];
+        for (int i=0;i<shu.length;i++){
+            if(min>shu[i]){
+                min=shu[i];
+                minshu=i;
+            }
+        }
+        zhuangzai=shu[shu.length-1];
+        shu[shu.length-1]=shu[minshu];
+        shu[minshu]=zhuangzai;
+        for(int i=0;i<shu.length;i++){
+            System.out.print(shu[i]+" ");
+        }
+    }
+}
+```
+
+
+
+用自定义函数实现求某数组元素和（大小不固定）。
+
+```java
+import java.util.Random;
+import java.util.Scanner;
+
+public class zy21 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("请输入多少位数组");
+        int[] shuzu = new int[sc.nextInt()];
+        System.out.println("请输入范围几到几");
+        int a = sc.nextInt();
+        int b = sc.nextInt();
+        Random ra = new Random();
+        for(int i=0;i<shuzu.length;i++){
+            shuzu[i]= ra.nextInt(b)+a;
+            System.out.print(shuzu[i]+" ");
+        }
+        sum(shuzu);
+
+    }
+    public static void sum(int[] shu) {
+        int sum=0;
+        for (int i=0;i< shu.length;i++){
+            sum+=shu[i];
+        }
+        System.out.println("\n数组和为："+sum);
+    }
+}
+```
+
+
+
+ 用户输入整数你，计算1!+（1!+2!）+（1!+2!+3!）+....+（1!+2!+....n!)
+
+```java
+public class zy22 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        System.out.println("请输入数字");
+        int a = sc.nextInt();
+        sum(a);
+
+    }
+    public static void sum(int shu) {
+        int count=0;
+        for (int i=1;i<=shu;i++){
+            System.out.print("(");
+            int sum=1;
+            for (int j=1;j<=i;j++){
+                if (i!=j) {
+                    System.out.print(j + "!"+"+");
+                }else{
+                    System.out.print(j + "!");
+                }
+                sum*=j;
+            }
+            count+=sum;
+            if (i!=shu) {
+                System.out.print(")" + "+");
+            }else{
+                System.out.print(")" );
+            }
+        }
+        System.out.println("="+count);
+    }
+}
+```
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