diff --git a/module02/ex04/main.c b/module02/ex04/main.c
index 16ac863..3650bb6 100644
--- a/module02/ex04/main.c
+++ b/module02/ex04/main.c
@@ -13,7 +13,6 @@
 // TIMER
 #define PERIOD				2000
 #define PRESCALE_VALUE		1024													// can be 1, 8, 64, 256, 1024
-#define STRLEN_LITERAL(str)			(sizeof(str) / sizeof(str[0]) - 1)						// -1 to remove the null terminator, only works with string literals, not with pointers
 
 // END MACROS
 
@@ -22,7 +21,10 @@ void uart_init();
 // char uart_rx(void);
 void uart_tx(char c);
 void uart_printstr(const char* str);
-void check_str(char input, volatile char compare_str[], unsigned int length);
+void remove_last_character();
+void fill_str(char input);
+int compare_str(volatile char *input_str, volatile char *base_str);
+int strlength(volatile char *str);
 void reset_message();
 void ask_for_username();
 void ask_for_password();
@@ -38,10 +40,8 @@ volatile char username[] = "admin";
 volatile char password[] = "password";
 volatile char username_input[100] = {0};
 volatile char password_input[100] = {0};
-
 volatile int input_index = 0;
 volatile State state = USERNAME;
-volatile int input_match = FALSE;
 volatile int username_correct = FALSE;
 volatile int password_correct = FALSE;
 
@@ -76,57 +76,43 @@ ISR(USART_RX_vect) {																// Table 12-7 : we select the code for USART
 	char received_char = UDR0;														// read received character
 	if (received_char == '\b' || received_char == 127) {							// if backspace is received
 		if (input_index <= 0) return;
+		remove_last_character();
 		input_index--;
 		uart_tx('\b');  // Move cursor back
 		uart_tx(' ');   // Erase the character on screen
 		uart_tx('\b');  // Move cursor back again
 	} else if (received_char == '\n' || received_char == '\r') {					// if enter is received
 		if (state == USERNAME) {
-			// if (input_index == STRLEN_LITERAL(username) && input_match) {
-			// 	username_correct = TRUE;
-			// } else {
-			// 	username_correct = FALSE;
-			// 	uart_printstr("(error1)");
-			// }
-
-			if (compare_str(username_input, username, STRLEN_LITERAL(username))) {
+			if (compare_str(username_input, username)) {
 				username_correct = TRUE;
 			} else {
 				username_correct = FALSE;
-				uart_printstr("(error1)");
+				// uart_printstr("(error1)");
 			}
-
-			input_match = FALSE;
 			state = PASSWORD;
 			input_index = 0;
-			uart_tx('\r');															// Move cursor to next line
+			uart_tx('\r');
 			uart_tx('\n');
 			ask_for_password();
 		} else if (state == PASSWORD) {
 			if (!username_correct) {
-				uart_printstr("(error2)");
+				// uart_printstr("(error2)");
 				return reset_message();
 			}
-			if (input_index != STRLEN_LITERAL(password)) {
-				uart_printstr("(error3)");
+			if (!compare_str(password_input, password)) {
+				// uart_printstr("(error3)");
 				return reset_message();
 			}
-			if (!input_match) {
-				uart_printstr("(error4)");
-				return reset_message();
-			}
-			uart_tx('\r');															// Move cursor to next line
+			uart_tx('\r');
 			uart_tx('\n');
 			on_success();
 		}
 	} else {
 		fill_str(received_char);
 		if (state == USERNAME) {
-			// check_str(received_char, username, STRLEN_LITERAL(username));
 			uart_tx(received_char);
 		}
 		else if (state == PASSWORD) {
-			// check_str(received_char, password, STRLEN_LITERAL(password));
 			uart_tx('*');
 		}
 		input_index++;
@@ -135,7 +121,7 @@ ISR(USART_RX_vect) {																// Table 12-7 : we select the code for USART
 
 void fill_str(char input) {
 	if (input_index >= 100) {
-		uart_printstr("(error8)");
+		// uart_printstr("(error4)");
 		return;
 	}
 	if (state == USERNAME) {
@@ -145,72 +131,49 @@ void fill_str(char input) {
 	}
 }
 
-int compare_str() {
-	char input_str[100] = {0};
-	char compare_str[100] = {0};
+void remove_last_character() {
 	if (state == USERNAME) {
-		compare_str = username;
-		input_str = username_input;
+		username_input[input_index] = 0;
 	} else if (state == PASSWORD) {
-		compare_str = password;
-		input_str = password_input;
+		password_input[input_index] = 0;
 	}
-	int length = STRLEN_LITERAL(compare_str);
-	int index = 0;
+}
 
-	while (*compare_str) {
-		if (index >= length) {
-			uart_printstr("(error5)");
-			return FALSE;
-		}
-		if (input_str[index] != *compare_str) {
-			uart_printstr("(error6)");
-			return FALSE;
-		}
-		compare_str++;
-		index++;
+int compare_str(volatile char *input_str, volatile char *base_str) {
+	int base_length = strlength(base_str);
+	int input_length = strlength(input_str);
+	if (base_length != input_length) {
+		// uart_printstr("(error5)");
+		return FALSE;
 	}
-
-	for (int i = 0; i < length; i++) {
-		if (input[i] != compare_str[i]) {
+	for(int i = 0; i < base_length; i++) {
+		if (input_str[i] != base_str[i]) {
+			// uart_printstr("(error6)");
 			return FALSE;
 		}
 	}
 	return TRUE;
 }
 
-void check_str(char input, volatile char compare_str[], unsigned int length) {
-	if (input_index >= length) {														// index has not already been incremented, so we need to compare greater or equal
-		uart_printstr("(error5)");
-		input_match = FALSE;
-		return;
+int strlength(volatile char *str) {
+	int length = 0;
+	while (*str) {
+		length++;
+		str++;
 	}
-	if (input != compare_str[input_index]) {
-		uart_printstr("(error6)");
-		input_match = FALSE;
-		return;
-	}
-	// if we reach this point, the input character matches the compare_str character
-	if (input_index == 0) {
-		input_match = TRUE;
-		return;
-	}
-	// if we reach this point, the input character is not the first character of the compare_str
-	if (input_match == FALSE) {
-		// if any previous character did not match, we don't need to check the next character
-		uart_printstr("(error7)");
-		return;
-	}
-	input_match = TRUE;
+	return length;
 }
 
 void reset_message() {
+	for(int i = 0; i < 100; i++) {
+		username_input[i] = 0;
+		password_input[i] = 0;
+	}
 	input_index = 0;
-	input_match = FALSE;
 	username_correct = FALSE;
 	password_correct = FALSE;
 	state = USERNAME;
-	uart_tx('\r');																// Move cursor to next line
+	uart_tx('\r');
 	uart_tx('\n');
 	on_error();
 	ask_for_username();