diff --git a/Exercise 3/Lexer.c b/Exercise 3/Lexer.c
new file mode 100644
index 0000000..12993d4
--- /dev/null
+++ b/Exercise 3/Lexer.c	
@@ -0,0 +1,28 @@
+#include "Lexer.h"
+
+int start(char* src) {
+    if (src != 0 && src != '\0') {      // checking if the string is empty or invalid
+        return _GET_NEXT_CHARACTER_;
+    }
+    return _STOP_;
+}
+
+int getNextCharacter(char* src) {
+    return _STOP_;                      // placeholder
+}
+
+int readIdentifier(char* src) {
+    return _STOP_;                      // placeholder
+}
+
+int readNumLit(char* src) {
+    return _STOP_;                      // placeholder
+}
+
+int readOperator(char* src) {
+    return _STOP_;                      // placeholder
+}
+
+int readPunctuation(char* src) {
+    return _STOP_;                      // placeholder
+}
diff --git a/Exercise 3/Lexer.h b/Exercise 3/Lexer.h
new file mode 100644
index 0000000..3e6fbe7
--- /dev/null
+++ b/Exercise 3/Lexer.h	
@@ -0,0 +1,26 @@
+/* symbols */
+#define _LETTER_ 1
+#define _DIGIT_ 2
+#define _OPERATOR_ 3
+#define _PUNCTUATION_ 4
+#define _END_OF_LINE_ 5
+#define _UNKNOWN_ 10
+
+/* state */
+#define _START_ 100
+#define _GET_NEXT_CHARACTER_ 110
+#define _READ_IDENTIFIER_ 120
+#define _READ_NUM_LIT_ 130
+#define _READ_OPERATOR_ 140
+#define _READ_PUNCTUATION_ 150
+#define _STOP_ 999
+#define _ERROR_ 1000
+
+/* functions */
+int start(char*);
+int getNextCharacter(char*);
+int readIdentifier(char*);
+int readNumLit(char*);
+int readOperator(char*);
+int readPunctuation(char*);
+int main();
diff --git a/Exercise 3/TestLexer.c b/Exercise 3/TestLexer.c
new file mode 100644
index 0000000..65e7559
--- /dev/null
+++ b/Exercise 3/TestLexer.c	
@@ -0,0 +1,42 @@
+#include <stdio.h>
+#include "Lexer.h"
+#include "Lexer.c"
+
+int main() {
+    // variables
+    char* sourcecode = "index = 2 * count + 42;";               // input string
+    int lexer_state = _START_;                                  // int var for the state machine
+
+    // checking var values
+    printf(sourcecode);                                         // printing the input string to check it
+
+    // main loop
+    do {
+        switch (lexer_state) {                                  // state machine starts here
+            case _START_:
+                lexer_state = start(sourcecode);
+                break;
+            case _GET_NEXT_CHARACTER_:
+                lexer_state = getNextCharacter(sourcecode);
+                break;
+            case _READ_IDENTIFIER_:
+                lexer_state = readIdentifier(sourcecode);
+                break;
+            case _READ_NUM_LIT_:
+                lexer_state = readNumLit(sourcecode);
+                break;
+            case _READ_OPERATOR_:
+                lexer_state = readOperator(sourcecode);
+                break;
+            case _READ_PUNCTUATION_:
+                lexer_state = readPunctuation(sourcecode);
+                break;
+            default: lexer_state = _ERROR_;
+        }
+    } while (lexer_state != _STOP_);                            // state machine ends here
+
+    // printf("Lexer exited with code ");
+    // printf(lexer_state);
+
+    return 0;
+}