diff --git a/.vscode/c_cpp_properties.json b/.vscode/c_cpp_properties.json
new file mode 100644
index 0000000..834113c
--- /dev/null
+++ b/.vscode/c_cpp_properties.json
@@ -0,0 +1,19 @@
+{
+    "configurations": [
+        {
+            "name": "Mac",
+            "includePath": [
+                "${workspaceFolder}/**"
+            ],
+            "defines": [],
+            "macFrameworkPath": [
+                "/Applications/Xcode.app/Contents/Developer/Platforms/MacOSX.platform/Developer/SDKs/MacOSX.sdk/System/Library/Frameworks"
+            ],
+            "compilerPath": "/usr/bin/clang",
+            "cStandard": "c17",
+            "cppStandard": "c++17",
+            "intelliSenseMode": "macos-clang-arm64"
+        }
+    ],
+    "version": 4
+}
\ No newline at end of file
diff --git a/.vscode/settings.json b/.vscode/settings.json
index d8cb326..7ae686b 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,5 +1,7 @@
 {
     "files.associations": {
-        "string": "cpp"
+        "string": "cpp",
+        "token.h": "c",
+        "token_type.h": "c"
     }
 }
\ No newline at end of file
diff --git a/Makefile b/Makefile
index 3cdc525..b080298 100644
--- a/Makefile
+++ b/Makefile
@@ -1,7 +1,7 @@
 all: output execute
 
 output:
-	gcc src/main.c -o build/main
+	gcc src/main.c src/utils/ints.c src/utils/strings.c src/lexer/lexer.c -o build/main
 
 execute:
 	./build/main
\ No newline at end of file
diff --git a/build/main b/build/main
index 013ca82..5a947f3 100755
Binary files a/build/main and b/build/main differ
diff --git a/src/common/types.h b/src/common/types.h
new file mode 100644
index 0000000..fb8b356
--- /dev/null
+++ b/src/common/types.h
@@ -0,0 +1,6 @@
+#ifndef COMMON_TYPES_H
+#define COMMON_TYPES_H
+
+typedef char* string;
+
+#endif // TCOMMON_YPES_H
\ No newline at end of file
diff --git a/src/lexer/lexer.c b/src/lexer/lexer.c
index 64b11d3..bdae384 100644
--- a/src/lexer/lexer.c
+++ b/src/lexer/lexer.c
@@ -1,8 +1,134 @@
 #ifndef LEXER_C
 #define LEXER_C
 
-#include "token.h"
-#include "token_type.h"
-#include "types.h"
+#include "token/token.h"
+#include "token/token_type.h"
+
+#include "../common/types.h"
+#include "../utils/strings.h"
+#include "../utils/ints.h"
+
+#include <string.h>
+#include <stdio.h>
+
+/**
+ * @brief Pushes a token to the back of a token array.
+ *
+ * @param tokens The token array.
+ * @param token The token to push.
+ */
+void push_back(Token tokens[], Token token)
+{
+    tokens[sizeof(tokens) + 1] = token;
+}
+
+/**
+ * @brief Pops a token from the front of a token array.
+ *
+ * @param tokens The token array.
+ * @return Token The popped token.
+ */
+string pop(string *tokens)
+{
+    string res = tokens[0];
+    for (int i = 1; i < sizeof(tokens); i++)
+    {
+        tokens[i - 1] = tokens[i];
+    }
+    return res;
+}
+
+/**
+ * @brief Tokenizes a string.
+ *
+ * @param src The string to tokenize.
+ * @return const Token* The tokens.
+ */
+Token *tokenize(string src)
+{
+    // The list of tokens
+    Token tokens[] = {};
+
+    // Split the src
+    string *split_src = split(src, " ");
+
+    // Build each token
+    while (sizeof(split_src) > 0)
+    {
+        // Pop the token
+        string token = pop(split_src);
+
+        // Check the token type
+        if (token == ' ' || token == '\n' || token == '\t')
+        {
+            continue;
+        }
+        else if (token == '(')
+        {
+            push_back(tokens, (Token){TOKEN_TYPE_LEFT_PAREN, "("});
+        }
+        else if (token == ')')
+        {
+            push_back(tokens, (Token){TOKEN_TYPE_RIGHT_PAREN, ")"});
+        }
+        else if (token == '=')
+        {
+            push_back(tokens, (Token){TOKEN_TYPE_EQUAL, "="});
+        }
+        else if (token == '+')
+        {
+            push_back(tokens, (Token){TOKEN_TYPE_PLUS, "+"});
+        }
+        else if (token == '-')
+        {
+            push_back(tokens, (Token){TOKEN_TYPE_MINUS, "-"});
+        }
+        else if (token == '*')
+        {
+            push_back(tokens, (Token){TOKEN_TYPE_MULTIPLY, "*"});
+        }
+        else if (token == '/')
+        {
+            Token token = {TOKEN_TYPE_DIVIDE, "/"};
+            push_back(tokens, token);
+        }
+        else
+        {
+            if (is_int(token))
+            {
+                string num = "";
+                while (sizeof(split_src) > 0 && is_int(split_src[0]))
+                {
+                    string n = pop(split_src);
+                    num = strcat(num, n);
+                }
+                push_back(tokens, (Token){TOKEN_TYPE_NUMBER, num});
+            }
+            else if (is_alpha(token))
+            {
+                string str = "";
+                while (sizeof(split_src) > 0 && is_alpha(split_src[0]))
+                {
+                    string n = pop(split_src);
+                    str = strcat(str, n);
+                }
+                if (token == "let")
+                {
+                    push_back(tokens, (Token){TOKEN_TYPE_LET, "let"});
+                }
+                else
+                {
+                    push_back(tokens, (Token){TOKEN_TYPE_IDENTIFIER, str});
+                }
+            }
+            else
+            {
+                return tokens;
+            }
+        }
+    }
+
+    return tokens;
+}
 
 #endif // LEXER_C
\ No newline at end of file
diff --git a/src/lexer/lexer.h b/src/lexer/lexer.h
index 9bc37ce..cf4cefe 100644
--- a/src/lexer/lexer.h
+++ b/src/lexer/lexer.h
@@ -1,5 +1,15 @@
-#ifndef LEXER_h
-#define LEXER_h
+#ifndef LEXER_H
+#define LEXER_H
 
+#include "token/token.h"
+#include "../common/types.h"
 
-#endif // LEXER_h
\ No newline at end of file
+/**
+ * @brief Tokenizes a string.
+ *
+ * @param src The string to tokenize.
+ * @return const Token* The tokens.
+ */
+Token *tokenize(string src);
+
+#endif // LEXER_H
\ No newline at end of file
diff --git a/src/lexer/token.h b/src/lexer/token/token.h
similarity index 90%
rename from src/lexer/token.h
rename to src/lexer/token/token.h
index ff791a9..5b3df39 100644
--- a/src/lexer/token.h
+++ b/src/lexer/token/token.h
@@ -2,7 +2,7 @@
 #define TOKEN_H
 
 #include "token_type.h"
-#include "types.h"
+#include "../../common/types.h"
 
 /**
  * @brief A token is a pair of a token type and a value.
diff --git a/src/lexer/token_type.h b/src/lexer/token/token_type.h
similarity index 98%
rename from src/lexer/token_type.h
rename to src/lexer/token/token_type.h
index 66737b8..30003cf 100644
--- a/src/lexer/token_type.h
+++ b/src/lexer/token/token_type.h
@@ -14,6 +14,7 @@
 typedef enum TokenType
 {
     TOKEN_TYPE_EOF,
+    TOKEN_TYPE_LET,
     TOKEN_TYPE_NUMBER,
     TOKEN_TYPE_PLUS,
     TOKEN_TYPE_MINUS,
diff --git a/src/lexer/types.h b/src/lexer/types.h
deleted file mode 100644
index f160bac..0000000
--- a/src/lexer/types.h
+++ /dev/null
@@ -1,6 +0,0 @@
-#ifndef TYPES_H
-#define TYPES_H
-
-typedef char* string;
-
-#endif // TYPES_H
\ No newline at end of file
diff --git a/src/main.c b/src/main.c
index 72b9b43..ee80b0b 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1,7 +1,14 @@
 #include <stdio.h>
 
+#include "lexer/lexer.h"
+#include "common/types.h"
+
 int main(void)
 {
-    printf("Hello, world!\n");
-    return 0;
+    string src = "let x = 5";
+    Token *tokens = tokenize(src);
+    for (int i = 0; i < sizeof(tokens); i++)
+    {
+        printf("Token: %s\n", tokens[i].value);
+    }
 }
\ No newline at end of file
diff --git a/src/main.simpl b/src/main.simpl
new file mode 100644
index 0000000..edacaa6
--- /dev/null
+++ b/src/main.simpl
@@ -0,0 +1 @@
+let x = 45
\ No newline at end of file
diff --git a/src/utils/ints.c b/src/utils/ints.c
new file mode 100644
index 0000000..78aa8ab
--- /dev/null
+++ b/src/utils/ints.c
@@ -0,0 +1,18 @@
+#ifndef UTILS_INTS_C
+#define UTILS_INTS_C
+
+#include <stdbool.h>
+
+/**
+ * @brief Checks if a character is an integer.
+ * 
+ * @param c The character to check.
+ * @return true If the character is an integer.
+ * @return false If the character is not an integer.
+ */
+bool is_int(char c)
+{
+    return c >= '0' && c <= '9';
+}
+
+#endif // UTILS_INTS_C
\ No newline at end of file
diff --git a/src/utils/ints.h b/src/utils/ints.h
new file mode 100644
index 0000000..f4a92cf
--- /dev/null
+++ b/src/utils/ints.h
@@ -0,0 +1,15 @@
+#ifndef UTILS_INTS_H
+#define UTILS_INTS_H
+
+#include <stdbool.h>
+
+/**
+ * @brief Checks if a character is an integer.
+ * 
+ * @param c The character to check.
+ * @return true If the character is an integer.
+ * @return false If the character is not an integer.
+ */
+bool is_int(char c);
+
+#endif // UTILS_INTS_H
\ No newline at end of file
diff --git a/src/utils/strings.c b/src/utils/strings.c
new file mode 100644
index 0000000..9c396f4
--- /dev/null
+++ b/src/utils/strings.c
@@ -0,0 +1,42 @@
+#ifndef UTILS_STRINGS_H
+#define UTILS_STRINGS_H
+
+#include "../common/types.h"
+
+#include <stdbool.h>
+#include <stdlib.h>
+#include <string.h>
+
+/**
+ * @brief Splits a string by a delimiter.
+ * 
+ * @param src The string to split.
+ * @param delim The delimiter to split by.
+ * @return string* The split string.
+ */
+string *split(string src, string delim)
+{
+    string *res = malloc(sizeof(string));
+    string token = strtok(src, delim);
+
+    while (token != NULL)
+    {
+        res[sizeof(res) + 1] = token;
+        token = strtok(NULL, delim);
+    }
+    return res;
+}
+
+/**
+ * @brief Checks if a character is a digit.
+ * 
+ * @param c The character to check.
+ * @return true If the character is a digit.
+ * @return false If the character is not a digit.
+ */
+bool is_alpha(char c)
+{
+    return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
+}
+
+#endif // UTILS_STRING_H
\ No newline at end of file
diff --git a/src/utils/strings.h b/src/utils/strings.h
new file mode 100644
index 0000000..908d3f4
--- /dev/null
+++ b/src/utils/strings.h
@@ -0,0 +1,25 @@
+#ifndef UTILS_STRINGS_H
+#define UTILS_STRINGS_H
+
+#include "../common/types.h"
+#include <stdbool.h>
+
+/**
+ * @brief Splits a string by a delimiter.
+ * 
+ * @param src The string to split.
+ * @param delim The delimiter to split by.
+ * @return string* The split string.
+ */
+string *split(string src, string delim);
+
+/**
+ * @brief Checks if a character is a digit.
+ * 
+ * @param c The character to check.
+ * @return true If the character is a digit.
+ * @return false If the character is not a digit.
+ */
+bool is_alpha(char c);
+
+#endif // UTILS_STRING_H
\ No newline at end of file