diff --git a/a b/a
new file mode 100644
index 0000000..e69de29
diff --git a/assignments/shell/TraverseDir/README.md b/assignments/shell/TraverseDir/README.md
new file mode 100644
index 0000000..45e8d09
--- /dev/null
+++ b/assignments/shell/TraverseDir/README.md
@@ -0,0 +1,3 @@
+杜伊涵 22920142203807
+shell作业：
+写一个shell脚本TraverseDir.sh遍历输出当前目录及其子目录下的所有文件和目录。
diff --git a/assignments/shell/TraverseDir/README.md~ b/assignments/shell/TraverseDir/README.md~
new file mode 100644
index 0000000..1349165
--- /dev/null
+++ b/assignments/shell/TraverseDir/README.md~
@@ -0,0 +1,3 @@
+杜伊涵 22920142203807
+shell作业：
+写一个shell脚本TraverseDir.sh遍历当前目录及其子目录下的所有文件和目录。
diff --git a/assignments/shell/TraverseDir/TraverseDir.sh b/assignments/shell/TraverseDir/TraverseDir.sh
new file mode 100755
index 0000000..386a8ad
--- /dev/null
+++ b/assignments/shell/TraverseDir/TraverseDir.sh
@@ -0,0 +1,15 @@
+#!/bin/bash
+function traverse_dir()
+{
+ for file in $1/*
+ do
+  if [ -d $file ]
+  then
+   traverse_dir $file
+  else
+   echo $file
+  fi
+ done
+}
+traverse_dir $PWD
+
diff --git a/experiments/gcc-1-hello-world/Makefile b/experiments/gcc-1-hello-world/Makefile
new file mode 100644
index 0000000..2e4bc12
--- /dev/null
+++ b/experiments/gcc-1-hello-world/Makefile
@@ -0,0 +1,6 @@
+main:main.o
+	gcc main.o -o main
+main.o:main.c
+	gcc -c main.c
+clean:
+	rm main *.o
diff --git a/experiments/gcc-1-hello-world/Makefile~ b/experiments/gcc-1-hello-world/Makefile~
new file mode 100644
index 0000000..e69de29
diff --git a/experiments/gcc-1-hello-world/mian b/experiments/gcc-1-hello-world/mian
new file mode 100755
index 0000000..ab0a53d
Binary files /dev/null and b/experiments/gcc-1-hello-world/mian differ
diff --git a/experiments/gcc-2-multi-source/Makefile b/experiments/gcc-2-multi-source/Makefile
new file mode 100644
index 0000000..0531065
--- /dev/null
+++ b/experiments/gcc-2-multi-source/Makefile
@@ -0,0 +1,9 @@
+main:main.o calculator.o
+	gcc main.o calculator.o -o main
+main.o:main.c
+	gcc -c main.c
+calculator.o:calculator.c
+	gcc -c calculator.c
+
+clean:
+	rm main *.o
diff --git a/experiments/gcc-2-multi-source/calculator.c b/experiments/gcc-2-multi-source/calculator.c
index 391fc7f..979fdaa 100644
--- a/experiments/gcc-2-multi-source/calculator.c
+++ b/experiments/gcc-2-multi-source/calculator.c
@@ -1,5 +1,5 @@
 #include "include/calculator.h"
-
+#include <stdio.h>
 int sum(int x, int y) {
 	return x + y;
 }
@@ -13,5 +13,10 @@ int multiply(int x, int y) {
 }
 
 int divide(int x, int divisor) {
-	return x / divisor;
+	if(divisor==0)
+	{
+		printf("Divisor cannot be 0!\n");
+		return -999999;
+	}
+	else	return x / divisor;
 }
diff --git a/experiments/gcc-2-multi-source/calculator.c~ b/experiments/gcc-2-multi-source/calculator.c~
new file mode 100644
index 0000000..979fdaa
--- /dev/null
+++ b/experiments/gcc-2-multi-source/calculator.c~
@@ -0,0 +1,22 @@
+#include "include/calculator.h"
+#include <stdio.h>
+int sum(int x, int y) {
+	return x + y;
+}
+
+int subtract(int x, int y) {
+	return x - y;
+}
+
+int multiply(int x, int y) {
+	return x * y;
+}
+
+int divide(int x, int divisor) {
+	if(divisor==0)
+	{
+		printf("Divisor cannot be 0!\n");
+		return -999999;
+	}
+	else	return x / divisor;
+}
diff --git a/experiments/gcc-2-multi-source/main b/experiments/gcc-2-multi-source/main
new file mode 100755
index 0000000..29b98f5
Binary files /dev/null and b/experiments/gcc-2-multi-source/main differ
diff --git a/experiments/gcc-2-multi-source/main.c b/experiments/gcc-2-multi-source/main.c
index bdbb5b9..dfb4d9a 100644
--- a/experiments/gcc-2-multi-source/main.c
+++ b/experiments/gcc-2-multi-source/main.c
@@ -7,6 +7,9 @@ int main(void) {
 	y = 3;
 
 	printf("%d + %d = %d\n", x, y, sum(2, 3));
-
+	printf("%d - %d = %d\n", x, y, subtract(2, 3));
+	printf("%d * %d = %d\n", x, y, multiply(2, 3));
+	printf("%d / %d = %d\n", x, y, divide(2, 3));
+	printf("1 / 0 = %d\n", divide(1, 0));
 	return 0;
 }
diff --git a/experiments/gcc-2-multi-source/main.c~ b/experiments/gcc-2-multi-source/main.c~
new file mode 100644
index 0000000..ba90d84
--- /dev/null
+++ b/experiments/gcc-2-multi-source/main.c~
@@ -0,0 +1,15 @@
+#include <stdio.h>
+
+int main(void) {
+	int x, y;
+	
+	x = 2;
+	y = 3;
+
+	printf("%d + %d = %d\n", x, y, sum(2, 3));
+	printf("%d - %d = %d\n", x, y, subtract(2, 3));
+	printf("%d * %d = %d\n", x, y, multiply(2, 3));
+	printf("%d / %d = %d\n", x, y, divide(2, 3));
+	printf("1  /  0 = %d\n", divide(1, 0));
+	return 0;
+}
diff --git a/experiments/gcc-3-real-project/calculator.c b/experiments/gcc-3-real-project/calculator.c
index 391fc7f..979fdaa 100644
--- a/experiments/gcc-3-real-project/calculator.c
+++ b/experiments/gcc-3-real-project/calculator.c
@@ -1,5 +1,5 @@
 #include "include/calculator.h"
-
+#include <stdio.h>
 int sum(int x, int y) {
 	return x + y;
 }
@@ -13,5 +13,10 @@ int multiply(int x, int y) {
 }
 
 int divide(int x, int divisor) {
-	return x / divisor;
+	if(divisor==0)
+	{
+		printf("Divisor cannot be 0!\n");
+		return -999999;
+	}
+	else	return x / divisor;
 }
diff --git a/experiments/gcc-3-real-project/calculator.c~ b/experiments/gcc-3-real-project/calculator.c~
new file mode 100644
index 0000000..6742d36
--- /dev/null
+++ b/experiments/gcc-3-real-project/calculator.c~
@@ -0,0 +1,22 @@
+#include "include/calculator.h"
+
+int sum(int x, int y) {
+	return x + y;
+}
+
+int subtract(int x, int y) {
+	return x - y;
+}
+
+int multiply(int x, int y) {
+	return x * y;
+}
+
+int divide(int x, int divisor) {
+	if(divisor==0)
+	{
+		printf("Divisor cannot be 0!\n");
+		return -999999;
+	}
+	else	return x / divisor;
+}
diff --git a/experiments/gcc-3-real-project/include/calculator.h b/experiments/gcc-3-real-project/include/calculator.h
index a5e00e3..2059a48 100644
--- a/experiments/gcc-3-real-project/include/calculator.h
+++ b/experiments/gcc-3-real-project/include/calculator.h
@@ -1,9 +1,5 @@
-#ifndef _CALC_H
-#define _CALC_H
-
 int sum(int x, int y);
 int subtract(int x, int y);
 int multiply(int x, int y);
 int divide(int x, int divisor);
 
-#endif //_CALC_H
diff --git a/experiments/gcc-3-real-project/include/calculator.h~ b/experiments/gcc-3-real-project/include/calculator.h~
new file mode 100644
index 0000000..a5e00e3
--- /dev/null
+++ b/experiments/gcc-3-real-project/include/calculator.h~
@@ -0,0 +1,9 @@
+#ifndef _CALC_H
+#define _CALC_H
+
+int sum(int x, int y);
+int subtract(int x, int y);
+int multiply(int x, int y);
+int divide(int x, int divisor);
+
+#endif //_CALC_H
diff --git a/experiments/gcc-3-real-project/main b/experiments/gcc-3-real-project/main
new file mode 100755
index 0000000..baa84ef
Binary files /dev/null and b/experiments/gcc-3-real-project/main differ
diff --git a/experiments/gcc-3-real-project/main.c b/experiments/gcc-3-real-project/main.c
index 6798996..cf88d70 100644
--- a/experiments/gcc-3-real-project/main.c
+++ b/experiments/gcc-3-real-project/main.c
@@ -8,7 +8,10 @@ int main(void) {
 	x = 2;
 	y = 3;
 
+	printf("%d + %d = %d\n", x, y, sum(2, 3));
 	printf("%d - %d = %d\n", x, y, subtract(2, 3));
-
+	printf("%d * %d = %d\n", x, y, multiply(2, 3));
+	printf("%d / %d = %d\n", x, y, divide(2, 3));
+	printf("1 / 0 = %d\n", divide(1, 0));
 	return 0;
 }
diff --git a/experiments/gcc-3-real-project/main.c~ b/experiments/gcc-3-real-project/main.c~
new file mode 100644
index 0000000..134313a
--- /dev/null
+++ b/experiments/gcc-3-real-project/main.c~
@@ -0,0 +1,17 @@
+#include <stdio.h>
+
+#include "include/calculator.h"
+
+int main(void) {
+	int x, y;
+	
+	x = 2;
+	y = 3;
+
+	printf("%d + %d = %d\n", x, y, sum(2, 3));
+	printf("%d - %d = %d\n", x, y, subtract(2, 3));
+	printf("%d * %d = %d\n", x, y, multiply(2, 3));
+	printf("%d / %d = %d\n", x, y, divide(2, 3));
+	printf("1  /  0 = %d\n", divide(1, 0));
+	return 0;
+}
diff --git a/experiments/gcc-4-optimize/calculator.c b/experiments/gcc-4-optimize/calculator.c
index 391fc7f..979fdaa 100644
--- a/experiments/gcc-4-optimize/calculator.c
+++ b/experiments/gcc-4-optimize/calculator.c
@@ -1,5 +1,5 @@
 #include "include/calculator.h"
-
+#include <stdio.h>
 int sum(int x, int y) {
 	return x + y;
 }
@@ -13,5 +13,10 @@ int multiply(int x, int y) {
 }
 
 int divide(int x, int divisor) {
-	return x / divisor;
+	if(divisor==0)
+	{
+		printf("Divisor cannot be 0!\n");
+		return -999999;
+	}
+	else	return x / divisor;
 }
diff --git a/experiments/gcc-4-optimize/include/array.h b/experiments/gcc-4-optimize/include/array.h
index 3f079f4..bef1e29 100644
--- a/experiments/gcc-4-optimize/include/array.h
+++ b/experiments/gcc-4-optimize/include/array.h
@@ -1,9 +1,7 @@
-#ifndef _ARRAY_H
-#define _ARRAY_H
+
 
 void array_fill_with(int *array, int length, int fillWith);
 void array_print(int *array, int length);
 
 void array_add(int *arrayX, int *arrayY, int *arrayZ, int length);
 
-#endif
diff --git a/experiments/gcc-4-optimize/include/array.h~ b/experiments/gcc-4-optimize/include/array.h~
new file mode 100644
index 0000000..3f079f4
--- /dev/null
+++ b/experiments/gcc-4-optimize/include/array.h~
@@ -0,0 +1,9 @@
+#ifndef _ARRAY_H
+#define _ARRAY_H
+
+void array_fill_with(int *array, int length, int fillWith);
+void array_print(int *array, int length);
+
+void array_add(int *arrayX, int *arrayY, int *arrayZ, int length);
+
+#endif
diff --git a/final-test/c_cpp/Makefile b/final-test/c_cpp/Makefile
index 8b13789..a156638 100644
--- a/final-test/c_cpp/Makefile
+++ b/final-test/c_cpp/Makefile
@@ -1 +1,10 @@
+main:my_stack.o main.o
+	gcc my_stack.o main.o -o main
+my_stack.o:
+	gcc -c my_stack.c
+main.o:
+	gcc -c main.c
+clean:
+	if [ -e main ];then rm main;fi;
+	rm *.o
 
diff --git a/final-test/c_cpp/Makefile~ b/final-test/c_cpp/Makefile~
new file mode 100644
index 0000000..dbb969b
--- /dev/null
+++ b/final-test/c_cpp/Makefile~
@@ -0,0 +1,10 @@
+main:my_stack.o main.o
+	gcc my_stack.o main.o -o main
+my_stack.o:
+	gcc -c my_stack.c
+main.o:
+	gcc -c main.c
+clean:
+	if [ -e main ];then rm main;fi;
+	if [ -e *.o ];then rm *.o;fi;
+
diff --git a/final-test/c_cpp/my_stack.c b/final-test/c_cpp/my_stack.c
index 3d461cb..b596a87 100644
--- a/final-test/c_cpp/my_stack.c
+++ b/final-test/c_cpp/my_stack.c
@@ -4,5 +4,40 @@
  * 但是记住g++才是编译C++的编译器
  *
  */
+#define MAXSIZE 5
+int s[MAXSIZE];
+int base=0,top=0;
+void stack_push(int x)
+{
+	s[top++]=x;
+}
+int stack_pop()
+{
+	int e;
+	e=s[--top];
+	return e;
+}
+// The capacity of the stack
+int stack_capacity()
+{
+	return MAXSIZE;
+}
+// Current available size of the stack
+int stack_size()
+{
+	return top-base;
+}
 
-
+/*
+ * return 0/1 to check if stack is empty or full
+ * 0 - No
+ * 1 - Yes
+ */
+int stack_is_empty()
+{
+	return top==base;
+}
+int stack_is_full()
+{
+	return stack_size()==MAXSIZE;
+}
diff --git a/final-test/c_cpp/my_stack.c~ b/final-test/c_cpp/my_stack.c~
new file mode 100644
index 0000000..46c73d6
--- /dev/null
+++ b/final-test/c_cpp/my_stack.c~
@@ -0,0 +1,43 @@
+/*
+ * my_stack的实现文件
+ * 如果采用C++的实现，那也可以把此文件名改为.cpp
+ * 但是记住g++才是编译C++的编译器
+ *
+ */
+#define MAXSIZE 100
+int s[MAXSIZE];
+int base=0,top=0;
+void stack_push(int x)
+{
+	s[top++]=x;
+}
+int stack_pop()
+{
+	int e;
+	e=s[--top];
+	return e;
+}
+// The capacity of the stack
+int stack_capacity()
+{
+	return MAXSIZE;
+}
+// Current available size of the stack
+int stack_size()
+{
+	return top-base;
+}
+
+/*
+ * return 0/1 to check if stack is empty or full
+ * 0 - No
+ * 1 - Yes
+ */
+int stack_is_empty()
+{
+	return top==base;
+}
+int stack_is_full()
+{
+	return stack_size()==MAXSIZE;
+}