diff --git a/bin/compiler.php b/bin/compiler.php
index a0222beb..90e3f8b0 100755
--- a/bin/compiler.php
+++ b/bin/compiler.php
@@ -15,6 +15,7 @@ $code = $translator->convert($file);
 $info = pathinfo($file);
 $cppFile = $info['dirname'] . '/' . $info['filename'] . '.cc';
 $translator->save($code, $cppFile);
+$translator->genFunctionDeclaration("./php_func_decl.h");
 $translator->compileFile($cppFile);
 
 $objectFile = $info['dirname'] . '/' . $info['filename'] . '.cc.o';
diff --git a/src/Php/ArgInfo.php b/src/Php/ArgInfo.php
index da894647..0bb403f3 100644
--- a/src/Php/ArgInfo.php
+++ b/src/Php/ArgInfo.php
@@ -6,5 +6,5 @@ class ArgInfo
 {
     public string $name;
     public string $type;
-    public string $default;
+    public string $default = '';
 }
\ No newline at end of file
diff --git a/src/Php/FunctionDef.php b/src/Php/FunctionDef.php
index 72c1e2da..6c5a2ede 100644
--- a/src/Php/FunctionDef.php
+++ b/src/Php/FunctionDef.php
@@ -5,7 +5,8 @@ namespace PhpAot\Php;
 class FunctionDef
 {
     public string $name;
-    public array $arguments;
+    public array $argInfoList = [];
+    public string $params;
     public string $returnType;
-    public int $argumentCountRequired = 0;
+    public int $argCountRequired = 0;
 }
\ No newline at end of file
diff --git a/src/Php/Reflection.php b/src/Php/Reflection.php
index 4be80fd6..d9f84aa6 100644
--- a/src/Php/Reflection.php
+++ b/src/Php/Reflection.php
@@ -11,7 +11,12 @@ class Reflection
     static function getFunction(string $fn)
     {
         if (!isset(self::$functions[$fn])) {
-            self::$functions[$fn] = new ReflectionFunction($fn);
+            try {
+                $ref = new ReflectionFunction($fn);;
+            } catch (\ReflectionException $e) {
+                return null;
+            }
+            self::$functions[$fn] = $ref;
         }
         return self::$functions[$fn];
     }
@@ -19,6 +24,9 @@ class Reflection
     static function getFunctionReturnType(string $fn): ?string
     {
         $func = self::getFunction($fn);
+        if (!$func) {
+            return null;
+        }
         $returnType = $func->getReturnType();
         if (!$returnType) {
             return null;
diff --git a/src/Php/Translator.php b/src/Php/Translator.php
index 0bba7e20..197609cf 100644
--- a/src/Php/Translator.php
+++ b/src/Php/Translator.php
@@ -40,9 +40,49 @@ class Translator extends \PhpAot\Core\Translator
 
     private array $headers = [
         'phpx.h',
-        'phpx_func.h'
+        'phpx_func.h',
+        'php_func_decl.h',
     ];
 
+    private array $reservedNames = [
+        'auto',
+        'break',
+        'case',
+        'catch',
+        'class',
+        'struct',
+        'const',
+        'continue',
+        'default',
+        'do',
+        'else',
+        'elseif',
+        'enum',
+        'extends',
+        'final',
+        'finally',
+        'for',
+        'function',
+        'global',
+        'if',
+        'int',
+        'double',
+        'float',
+        'false',
+        'for',
+        'if',
+        'int',
+        'new',
+        'null',
+        'or',
+        'and',
+        'private',
+        'protected',
+        'public',
+        'return',
+        'static',
+     ];
+
     private array $internalFunctions = [];
 
     private int $optimizeLevel = 0;
@@ -315,15 +355,17 @@ class Translator extends \PhpAot\Core\Translator
             } else {
                 $this->functionDef->returnType = 'void';
             }
+            $this->parseParams($v->params);
             $this->internalFunctions[$name] = $this->functionDef;
         }
 
-        $params = $this->parseParams($v->params);
         $this->indentLevel++;
         $stmts = $this->parseStmts($v->stmts);
         $this->indentLevel--;
 
-        $code = $this->getReturnType() . ' ' . self::PREFIX . $name . '(' . $params . ') {' . PHP_EOL;
+        $functionDeclCode = $this->getReturnType() . ' ' . self::PREFIX . $name . '(' . $this->functionDef->params . ')';
+
+        $code = $functionDeclCode . ' {' . PHP_EOL;
         $this->indentLevel++;
         foreach ($this->localVars as $name => $type) {
             if (isset($this->arguments[$name])) {
@@ -358,7 +400,7 @@ class Translator extends \PhpAot\Core\Translator
             case 'Name':
             case 'Identifier':
             case 'Expr_Variable':
-                return $expr->name;
+                return $this->escapeVarName($expr->name);
             case 'Scalar_Int':
                 return $expr->value . 'L';
             case 'Scalar_Float':
@@ -372,10 +414,10 @@ class Translator extends \PhpAot\Core\Translator
         }
     }
 
-    private function parseParams($params): string
+    private function parseParams($params): void
     {
         $list = [];
-        $this->functionDef->argumentCountRequired = count($params);
+        $this->functionDef->argCountRequired = count($params);
         foreach ($params as $param) {
             $type = $this->parseType($param->type);
             $name = $this->parseIdentifier($param->var);
@@ -387,12 +429,12 @@ class Translator extends \PhpAot\Core\Translator
             $argInfo->name = $name;
             $argInfo->type = $type;
             if (isset($param->default)) {
-                $this->functionDef->argumentCountRequired = count($list) - 1;
+                $this->functionDef->argCountRequired = count($list) - 1;
                 $argInfo->default = $param->default->getAttribute('rawValue');
             }
-            $this->functionDef->arguments[] = $argInfo;
+            $this->functionDef->argInfoList[] = $argInfo;
         }
-        return implode(', ', $list);
+        $this->functionDef->params = implode(', ', $list);
     }
 
     private function parseStmts(array $stmts): string
@@ -905,6 +947,7 @@ class Translator extends \PhpAot\Core\Translator
     {
         $list = [
             $this->phpxDir . '/include',
+            './',
         ];
         $out = '$(php-config --includes) ';
         foreach ($list as $li) {
@@ -941,6 +984,7 @@ class Translator extends \PhpAot\Core\Translator
 
     private function addCompilationOption(string &$cmd): void
     {
+        $cmd .= $this->parseIncludes();
         $cmd .= ' -O' . $this->optimizeLevel;
         $cmd .= ' -g';
         if ($this->climate->arguments->defined('profile')) {
@@ -951,7 +995,7 @@ class Translator extends \PhpAot\Core\Translator
 
     public function compileFile($file): void
     {
-        $cmd = $this->cppCompiler . ' -c ' . $file . ' -o ' . $file . '.o ' . $this->parseIncludes();
+        $cmd = $this->cppCompiler . ' -c ' . $file . ' -o ' . $file . '.o ';
         $this->addCompilationOption($cmd);
         $this->climate->comment($cmd);
         shell_exec($cmd);
@@ -963,7 +1007,7 @@ class Translator extends \PhpAot\Core\Translator
         if ($this->climate->arguments->defined('output')) {
             $targetFile = $this->climate->arguments->get('output');
         }
-        $cmd = $this->cppCompiler . ' main.cc global_vars.cc ' . $objectFile . ' -o ' . $targetFile . ' ' . $this->parseIncludes() . $this->parseLdflags() . $this->parseLibs();
+        $cmd = $this->cppCompiler . ' main.cc global_vars.cc ' . $objectFile . ' -o ' . $targetFile . ' ' . $this->parseLdflags() . $this->parseLibs();
         $this->addCompilationOption($cmd);
         $this->climate->comment($cmd);
         shell_exec($cmd);
@@ -1518,6 +1562,15 @@ class Translator extends \PhpAot\Core\Translator
         return addcslashes($str, "\\\"\n\r\t\v\f\0\x01..\x1f\x7f..\xff");
     }
 
+    private function escapeVarName(string $name): string
+    {
+        if (in_array($name, $this->reservedNames)) {
+            return '_php__var__' . $name;
+        } else {
+            return $name;
+        }
+    }
+
     private function parseInterpolatedStringPart(Node $expr): string
     {
         return '"' . $this->escapeString($expr->value) . '"';
@@ -1536,7 +1589,7 @@ class Translator extends \PhpAot\Core\Translator
     private function getArgInfo(string $funcName, int $index): ArgInfo
     {
         $funcDef = $this->internalFunctions[$funcName];
-        return $funcDef->arguments[$index];
+        return $funcDef->argInfoList[$index];
     }
 
     private function getReturnType(): string
@@ -1857,4 +1910,29 @@ class Translator extends \PhpAot\Core\Translator
         }
         return $expr;
     }
+
+    public function genFunctionDeclaration(string $file): void
+    {
+        $code = '';
+        /**
+         * @var FunctionDef $func
+         */
+        foreach ($this->internalFunctions as $name => $func) {
+            $code .= 'extern ' . $func->returnType . ' ' . self::PREFIX . $name . '(';
+            $argInfoList = $func->argInfoList;
+            if ($argInfoList) {
+                $list = [];
+                foreach ($argInfoList as $argInfo) {
+                    $arg = $argInfo->type . ' ' . $argInfo->name;
+                    if ($argInfo->default) {
+                        $arg .= ' = ' . $argInfo->default;
+                    }
+                    $list[] = $arg;
+                }
+                $code .= implode(', ', $list);
+            }
+            $code .= ');' . PHP_EOL;
+        }
+        file_put_contents($file, $code);
+    }
 }
diff --git a/tests/aot/functions.phpt b/tests/aot/functions.phpt
new file mode 100644
index 00000000..a9c5f088
--- /dev/null
+++ b/tests/aot/functions.phpt
@@ -0,0 +1,93 @@
+--TEST--
+User-defined and Built-in Functions
+--FILE--
+<?php
+// Test user-defined function
+function add($a, $b) {
+    return $a + $b;
+}
+
+function multiply($x, $y) {
+    return $x * $y;
+}
+
+function greet($name) {
+    return "Hello, " . $name . "!";
+}
+
+function main() {
+    // Test function calls
+    $result1 = add(5, 3);
+    var_dump($result1);
+
+    $result2 = multiply(4, 7);
+    var_dump($result2);
+
+    $result3 = greet("World");
+    var_dump($result3);
+
+    // Test built-in functions
+    $test_string = "  Hello World  ";
+    $trimmed = trim($test_string);
+    var_dump($trimmed);
+
+    $upper = strtoupper($test_string);
+    var_dump($upper);
+
+    $len = strlen($trimmed);
+    var_dump($len);
+
+    // Test array functions
+    $numbers = [1, 2, 3, 4, 5];
+    $reversed = array_reverse($numbers);
+    var_dump($reversed);
+
+    $count = count($numbers);
+    var_dump($count);
+    $fact5 = factorial(5);
+    var_dump($fact5);
+
+    $greeting1 = greet_with_title("Smith");
+    var_dump($greeting1);
+
+    $greeting2 = greet_with_title("Jane", "Ms.");
+    var_dump($greeting2);
+}
+
+// Test recursive function
+function factorial($n) {
+    if ($n <= 1) {
+        return 1;
+    }
+    return $n * factorial($n - 1);
+}
+
+// Test function with default parameters
+function greet_with_title($name, $title = "Mr.") {
+    return $title . " " . $name;
+}
+
+?>
+--EXPECT--
+int(8)
+int(28)
+string(13) "Hello, World!"
+string(11) "Hello World"
+string(15) "  HELLO WORLD  "
+int(11)
+array(5) {
+  [0]=>
+  int(5)
+  [1]=>
+  int(4)
+  [2]=>
+  int(3)
+  [3]=>
+  int(2)
+  [4]=>
+  int(1)
+}
+int(5)
+int(120)
+string(9) "Mr. Smith"
+string(8) "Ms. Jane"
\ No newline at end of file
diff --git a/tests/aot/math_functions.phpt b/tests/aot/math_functions.phpt
new file mode 100644
index 00000000..02b02e64
--- /dev/null
+++ b/tests/aot/math_functions.phpt
@@ -0,0 +1,140 @@
+--TEST--
+Mathematical Functions
+--FILE--
+<?php
+// Test basic math functions
+$abs = abs(-5);
+var_dump($abs);
+
+$abs_float = abs(-3.7);
+var_dump($abs_float);
+
+// Test ceil and floor
+$ceil = ceil(4.2);
+var_dump($ceil);
+
+$floor = floor(4.8);
+var_dump($floor);
+
+$round = round(4.567, 2);
+var_dump($round);
+
+// Test min and max
+$min = min(3, 7, 1, 9, 4);
+var_dump($min);
+
+$max = max(3, 7, 1, 9, 4);
+var_dump($max);
+
+// Test with arrays
+$numbers = [5, 2, 8, 1, 9];
+$min_arr = min($numbers);
+var_dump($min_arr);
+
+$max_arr = max($numbers);
+var_dump($max_arr);
+
+// Test pow function
+$power = pow(2, 8);
+var_dump($power);
+
+// Test sqrt
+$sqrt = sqrt(64);
+var_dump($sqrt);
+
+$sqrt_float = sqrt(2);
+var_dump($sqrt_float);
+
+// Test rand and mt_rand (within a range for predictability)
+srand(12345); // For predictable results in tests
+$rand1 = rand(1, 100);
+var_dump($rand1);
+
+mt_srand(12345); // For predictable results in tests
+$rand2 = mt_rand(1, 100);
+var_dump($rand2);
+
+// Test number format
+$number = 1234.5678;
+$formatted = number_format($number, 2);
+var_dump($formatted);
+
+// Test fmod
+$fmod = fmod(10.5, 3.2);
+var_dump($fmod);
+
+// Test trigonometric functions
+$sin = sin(pi()/2); // Should be 1
+var_dump($sin);
+
+$cos = cos(0); // Should be 1
+var_dump($cos);
+
+$tan = tan(pi()/4); // Should be close to 1
+var_dump($tan);
+
+// Test logarithmic functions
+$log = log(M_E); // Natural log of e should be 1
+var_dump($log);
+
+$log10 = log10(100); // Base-10 log of 100 should be 2
+var_dump($log10);
+
+// Test exponential
+$exp = exp(1); // e^1 should be e
+var_dump($exp);
+
+// Test is_* functions
+$int_val = 42;
+$float_val = 3.14;
+$str_val = "hello";
+
+var_dump(is_int($int_val));
+var_dump(is_float($float_val));
+var_dump(is_numeric("123"));
+var_dump(is_numeric("abc"));
+
+// Test conversion functions
+$hex = dechex(255);
+var_dump($hex);
+
+$bin = decbin(8);
+var_dump($bin);
+
+$oct = decoct(8);
+var_dump($oct);
+
+$back_to_dec = hexdec($hex);
+var_dump($back_to_dec);
+?>
+--EXPECT--
+int(5)
+float(3.7)
+float(5)
+float(4)
+float(4.57)
+int(1)
+int(9)
+int(1)
+int(9)
+int(256)
+float(8)
+float(1.4142135623730951)
+int(91)
+int(91)
+string(8) "1,234.57"
+float(0.8999999999999995)
+float(1)
+float(1)
+float(0.9999999999999999)
+float(1)
+float(2)
+float(2.718281828459045)
+bool(true)
+bool(true)
+bool(true)
+bool(false)
+string(2) "ff"
+string(4) "1000"
+string(2) "10"
+int(255)
diff --git a/tests/aot/string_functions.phpt b/tests/aot/string_functions.phpt
new file mode 100644
index 00000000..124a02e6
--- /dev/null
+++ b/tests/aot/string_functions.phpt
@@ -0,0 +1,156 @@
+--TEST--
+String Functions
+--FILE--
+<?php
+// Test basic string functions
+$str = "Hello, World!";
+
+$len = strlen($str);
+var_dump($len);
+
+$upper = strtoupper($str);
+var_dump($upper);
+
+$lower = strtolower($str);
+var_dump($lower);
+
+// Test substr
+$substr = substr($str, 0, 5);
+var_dump($substr);
+
+$substr2 = substr($str, 7);
+var_dump($substr2);
+
+// Test strpos
+$pos = strpos($str, "World");
+var_dump($pos);
+
+// Test str_replace
+$replaced = str_replace("World", "PHP", $str);
+var_dump($replaced);
+
+// Test trim functions
+$spaced = "  Hello, World!  ";
+$trimmed = trim($spaced);
+var_dump($trimmed);
+
+$ltrimmed = ltrim($spaced);
+var_dump($ltrimmed);
+
+$rtrimmed = rtrim($spaced);
+var_dump($rtrimmed);
+
+// Test string concatenation
+$part1 = "Hello";
+$part2 = "World";
+$concatenated = $part1 . " " . $part2 . "!";
+var_dump($concatenated);
+
+// Test explode and implode
+$csv = "apple,banana,orange";
+$fruits = explode(",", $csv);
+var_dump($fruits);
+
+$joined = implode("-", $fruits);
+var_dump($joined);
+
+// Test comparison functions
+$cmp1 = strcmp("abc", "abc");
+var_dump($cmp1);
+
+$cmp2 = strcmp("abc", "def");
+var_dump($cmp2);
+
+$cmp3 = strcasecmp("ABC", "abc");
+var_dump($cmp3);
+
+// Test string formatting
+$formatted = sprintf("Value: %d, Text: %s", 42, "hello");
+var_dump($formatted);
+
+// Test chunk split
+$chunked = str_split("abcdefghij", 3);
+var_dump($chunked);
+
+// Test strrev
+$reversed = strrev("hello");
+var_dump($reversed);
+
+// Test word functions
+$word_count = str_word_count("Hello world!");
+var_dump($word_count);
+
+// Test ucfirst and ucwords
+$mixed_case = "hello world from PHP";
+$first_upper = ucfirst($mixed_case);
+var_dump($first_upper);
+
+$title_case = ucwords($mixed_case);
+var_dump($title_case);
+
+// Test number conversion from string
+$num_str = "123";
+$num = (int)$num_str;
+var_dump($num);
+
+$float_str = "45.67";
+$float = (float)$float_str;
+var_dump($float);
+
+// Test string padding
+$padded = str_pad("Hello", 10, "0", STR_PAD_LEFT);
+var_dump($padded);
+
+// Test string repeat
+$repeated = str_repeat("xy", 4);
+var_dump($repeated);
+
+// Test strip_tags
+$html = "<p>Hello <b>World</b>!</p>";
+$stripped = strip_tags($html);
+var_dump($stripped);
+?>
+--EXPECT--
+int(13)
+string(13) "HELLO, WORLD!"
+string(13) "hello, world!"
+string(5) "Hello"
+string(6) "World!"
+int(7)
+string(11) "Hello, PHP!"
+string(13) "Hello, World!"
+string(15) "Hello, World!  "
+string(15) "  Hello, World!"
+string(12) "Hello World!"
+array(3) {
+  [0]=>
+  string(5) "apple"
+  [1]=>
+  string(6) "banana"
+  [2]=>
+  string(6) "orange"
+}
+string(19) "apple-banana-orange"
+int(0)
+int(-3)
+int(0)
+string(22) "Value: 42, Text: hello"
+array(4) {
+  [0]=>
+  string(3) "abc"
+  [1]=>
+  string(3) "def"
+  [2]=>
+  string(3) "ghi"
+  [3]=>
+  string(1) "j"
+}
+string(5) "olleh"
+int(2)
+string(20) "Hello world from PHP"
+string(20) "Hello World From PHP"
+int(123)
+float(45.67)
+string(10) "00000Hello"
+string(8) "xyxyxyxy"
+string(12) "Hello World!"