add class-3 class-4 code.

Code/class-3/echo.c

@@ -0,0 +1,32 @@
+/*
+ * =====================================================================================
+ *
+ *       Filename:  echo.c
+ *
+ *    Description:  echo 
+ *
+ *        Version:  1.0
+ *        Created:  10/21/2011 09:14:08 PM
+ *       Revision:  none
+ *       Compiler:  gcc
+ *
+ *         Author:  Fu Haiping
+ *        Company:  ICT
+ *
+ * =====================================================================================
+ */
+/* Echo Line */
+#include <stdio.h>
+void echo()
+{
+	char buf[4];
+	gets(buf);
+	puts(buf);
+}
+
+int main(int argc, const char *argv[])
+{
+	echo();
+	return 0;
+}
+

Code/class-3/exploit.c

@@ -0,0 +1,42 @@
+/*
+ * =====================================================================================
+ *
+ *       Filename:  exploit.c
+ *
+ *    Description:  simple exploit
+ *
+ *        Version:  1.0
+ *        Created:  10/21/2011 09:19:42 PM
+ *       Revision:  none
+ *       Compiler:  gcc
+ *
+ *         Author:  Fu Haiping
+ *        Company:  ICT
+ *
+ * =====================================================================================
+ */
+
+#include <stdio.h>
+
+void echo()
+{
+	printf("hello in echo.\n");
+}
+
+
+void callee()
+{
+	printf("hello in caller.\n");
+}
+void caller()
+{
+	int dummy[3];
+	callee();
+	printf("done in callee.\n");
+}
+
+int main(int argc, const char * argv[])
+{
+	caller();
+	return 0;
+}

Code/class-4/time-consume.c

@@ -0,0 +1,57 @@
+/*
+ * =====================================================================================
+ *
+ *       Filename:  time-consume.c
+ *
+ *    Description:  a time-comsuming application.
+ *
+ *        Version:  1.0
+ *        Created:  10/25/2011 10:07:20 AM
+ *       Revision:  r1
+ *       Compiler:  gcc
+ *
+ *         Author:  Fu Haiping
+ *        Company:  ICT
+ *
+ * =====================================================================================
+ */
+#include <stdio.h>
+#include <stdlib.h>
+#include <unistd.h>
+
+int a(void) 
+{
+    int i=0,g=0;
+    while(i++<100000)
+    {
+        g+=i;
+    }
+    return g;
+}
+
+int b(void) 
+{
+    int i=0,g=0;
+    while(i++<400000)
+    {
+        g+=i;
+    }
+    return g;
+}
+int main(int argc, char** argv)
+{
+    int iterations;
+    if(argc != 2)
+    {
+        printf("Usage %s <No of Iterations>\n", argv[0]);
+        exit(-1);
+    }
+    else
+        iterations = atoi(argv[1]);
+    printf("No of iterations = %d\n", iterations);
+    while(iterations--)
+    {
+        a();
+        b();
+    }
+}