add ciphers (#6)

Author: realDuYuanChao

CMakeLists.txt

@@ -4,6 +4,7 @@ project(Examples C)
 
 set(CMAKE_C_STANDARD 99)
 
+add_subdirectory(ciphers)
 add_subdirectory(conversions)
 add_subdirectory(dynamicprogramming)
 add_subdirectory(maths)

ciphers/CMakeLists.txt

@@ -0,0 +1,13 @@
+# If necessary, use the RELATIVE flag, otherwise each source file may be listed
+# with full pathname. RELATIVE may makes it easier to extract an executable name
+# automatically.
+file( GLOB APP_SOURCES RELATIVE ${CMAKE_CURRENT_SOURCE_DIR} *.c )
+# file( GLOB APP_SOURCES ${CMAKE_SOURCE_DIR}/*.c )
+# AUX_SOURCE_DIRECTORY(${CMAKE_CURRENT_SOURCE_DIR} APP_SOURCES)
+foreach( testsourcefile ${APP_SOURCES} )
+    # I used a simple string replace, to cut off .cpp.
+    string( REPLACE ".c" "" testname ${testsourcefile} )
+    add_executable( ${testname} ${testsourcefile} )
+    install(TARGETS ${testname} DESTINATION "bin/ciphers")
+
+endforeach( testsourcefile ${APP_SOURCES} )

ciphers/caesar.c

@@ -0,0 +1,55 @@
+#include <assert.h>
+#include <string.h>
+
+/**
+ *
+ * @param original the origin text.
+ * @param steps the steps to be moved.
+ * @return the string encrypted.
+ */
+char *encrypt(char *original, int steps) {
+    for (int i = 0; original[i] != '\0'; ++i) {
+        if (original[i] >= 'A' && original[i] <= 'Z') {
+            original[i] = (char) ('A' + (original[i] - 'A' + steps) % 26);
+        } else if (original[i] >= 'a' && original[i] <= 'z') {
+            original[i] = (char) ('a' + (original[i] - 'a' + steps) % 26);
+        }
+    }
+    return original;
+}
+
+/**
+ * Decrypt a string.
+ * @param password the password to be decrypted.
+ * @param steps the steps to be moved.
+ * @return the string decrypted.
+ */
+char *decrypt(char *password, int steps) {
+    for (int i = 0; password[i] != '\0'; ++i) {
+        if (password[i] >= 'A' && password[i] <= 'Z') {
+            password[i] = (char) ('A' + (password[i] - 'A' - steps + 26) % 26);
+        } else if (password[i] >= 'a' && password[i] <= 'z') {
+            password[i] = (char) ('a' + (password[i] - 'a' - steps + 26) % 26);
+        }
+    }
+    return password;
+}
+
+void test() {
+    char original[100] = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
+    assert(strcmp("DEFGHIJKLMNOPQRSTUVWXYZABC", encrypt(original, 3)) == 0);
+
+    strcpy(original, "abcdefghijklmnopqrstuvwxyz");
+    assert(strcmp("defghijklmnopqrstuvwxyzabc", encrypt(original, 3)) == 0);
+
+    char password[100] = "DEFGHIJKLMNOPQRSTUVWXYZABC";
+    assert(strcmp("ABCDEFGHIJKLMNOPQRSTUVWXYZ", decrypt(password, 3)) == 0);
+
+    strcpy(password, "defghijklmnopqrstuvwxyzabc");
+    assert(strcmp("abcdefghijklmnopqrstuvwxyz", decrypt(password, 3)) == 0);
+}
+
+int main() {
+    test();
+    return 0;
+}