Redesigned everithing so that everything is cleaner and not making everything all messy to fix later, still, ther may be redesigns and shit but should be fine

include/lexer.h

@@ -0,0 +1,68 @@
+#ifndef LEXER_H
+#define LEXER_H
+
+#include <stddef.h>
+#include <stdbool.h>
+
+// For identifing
+typedef enum {
+    NODE_NUMBER,
+    NODE_OPERATOR,
+} ASTNodeType;
+
+// For classify operators
+typedef enum {
+    OP_ADD,
+    OP_SUB,
+    OP_MUL,
+    OP_DIV
+} Operator;
+
+typedef enum {
+    ARRAY_OK = 0,
+    ARRAY_EMPTY,
+    ARRAY_OUT_OF_BOUNDS,
+    ARRAY_NULL_ARG,
+} ASTNodeArrayErr;
+
+typedef enum {
+    LEXER_OK = 0,
+    LEXER_FAILED_NUMBER_CONVERSION,
+    LEXER_NOT_RECOGNIZED_SYMBOL,
+    LEXER_EMPTY_INPUT,
+    LEXER_NULL_ARG,
+    LEXER_WRONG_SYNTAX,
+} LexerErr;
+
+// Can be thought as tokens, they will be used by the parser.
+typedef struct ASTNode {
+    ASTNodeType type;
+    union {
+        double number;
+        struct ASTNode *left;
+        struct ASTNode *right;
+        Operator op;
+    } operator;
+} ASTNode;
+
+// I prefer ot have a dynamic array for storing the "tokens"
+typedef struct {
+    size_t len;
+    size_t cap;
+    ASTNode *data;
+} ASTNodeArray;
+
+// Basic array functionality
+ASTNodeArray ASTNodeArray_init(size_t size);
+void ASTNodeArray_free(ASTNodeArray *arr);
+ASTNodeArrayErr ASTNodeArray_push(ASTNodeArray arr, ASTNode node);
+ASTNodeArrayErr ASTNodeArray_get(const ASTNodeArray arr, size_t index, ASTNode *out);
+// Out in pop can be NULL so it doesn't return anything
+ASTNodeArrayErr ASTNodeArray_pop(ASTNodeArray arr, size_t index, ASTNode *out);
+
+// Lexer funtions as well as few functionality
+LexerErr tokenize(const char* input, ASTNodeArray *out);
+LexerErr tokenize_number(const char* input, size_t *offset, ASTNode *out);
+LexerErr string_to_number(const char* str, double *number);
+
+#endif // !LEXER_H

src/lexer.c

@@ -0,0 +1,8 @@
+#include "lexer.h"
+
+// Helps  state machine for the lexer :)
+typedef enum {
+    WAIT_FOR_NUMBER,
+    WAIT_FOR_OPERATOR,
+} LexerState;
+