diff --git a/C02 Expresion/src/NumberProcessor.java b/C02 Expresion/src/NumberProcessor.java
index 67a0693..c573610 100644
--- a/C02 Expresion/src/NumberProcessor.java	
+++ b/C02 Expresion/src/NumberProcessor.java	
@@ -5,10 +5,10 @@ public class NumberProcessor {
         Scanner sc = new Scanner(System.in);
         System.out.println("请输入一个三位或四位整数");
         int number = sc.nextInt();
-        if(number%100>0 && number%100<10){
+        if(number%100>0 && number%100<99){
             while(number>0){
                 System.out.println(number%10);
-                number=number/10;
+                number = number / 10;
             }
         } else if(number<0)
             System.out.println("请重新输入一个正整数");
diff --git a/C03 ControlFlow/src/EncryptDemo.java b/C03 ControlFlow/src/EncryptDemo.java
new file mode 100644
index 0000000..1652e09
--- /dev/null
+++ b/C03 ControlFlow/src/EncryptDemo.java	
@@ -0,0 +1,26 @@
+import java.util.Scanner;
+import java.util.Arrays;
+
+public class EncryptDemo {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+        String str = sc.nextLine();
+
+        byte key = sc.nextByte();
+        char[] enc= new char[str.length()];
+        for(int i=0;i<str.length();i++)
+            enc[i] =(char)(str.charAt(i) ^ key);
+
+//        for(char c:enc)
+//            System.out.print(c);
+        System.out.println(Arrays.toString(enc));
+
+        char[] dec= new char[enc.length];
+        for(int i=0;i<str.length();i++)
+            dec[i] =(char)(enc[i] ^ key);
+
+//        for(char c:dec)
+//            System.out.print(c);
+        System.out.println(Arrays.toString(dec));
+    }
+}