diff --git a/CMakeLists.txt b/CMakeLists.txt
index d5f3dea..cb5af47 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1,5 +1,5 @@
 cmake_minimum_required(VERSION 3.10)
-project(fun VERSION 0.37.41 LANGUAGES C)
+project(fun VERSION 0.37.42 LANGUAGES C)
 
 set(CMAKE_C_STANDARD 99)
 set(CMAKE_C_STANDARD_REQUIRED ON)
@@ -468,6 +468,12 @@ if(Threads_FOUND)
   target_link_libraries(fun_core PUBLIC Threads::Threads)
 endif()
 
+# Link libm for C99 math functions if available
+find_library(M_LIB m)
+if(M_LIB)
+  target_link_libraries(fun_core PUBLIC ${M_LIB})
+endif()
+
 # Interpreter /usr/bin/fun
 option(FUN_WITH_REPL "Enable interactive REPL in the fun CLI" OFF)
 add_executable(fun
diff --git a/examples/math_ceil.fun b/examples/math_ceil.fun
new file mode 100644
index 0000000..5c2ef16
--- /dev/null
+++ b/examples/math_ceil.fun
@@ -0,0 +1,36 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+// Demo of C99-like ceil(x)
+
+print("=== math ceil demo start ===")
+
+print("ceil(3.2) -> " + to_string(ceil(3.2)))       // 4
+print("ceil(3.0) -> " + to_string(ceil(3.0)))       // 3
+print("ceil(-3.2) -> " + to_string(ceil(-3.2)))     // -3
+print("ceil(-3.0) -> " + to_string(ceil(-3.0)))     // -3
+print("ceil(0.5) -> " + to_string(ceil(0.5)))       // 1
+print("ceil(-0.5) -> " + to_string(ceil(-0.5)))     // 0
+
+print("=== math ceil demo end ===")
+
+/* Expected output (values):
+=== math ceil demo start ===
+ceil(3.2) -> 4
+ceil(3.0) -> 3
+ceil(-3.2) -> -3
+ceil(-3.0) -> -3
+ceil(0.5) -> 1
+ceil(-0.5) -> 0
+=== math ceil demo end ===
+*/
diff --git a/examples/math_floor.fun b/examples/math_floor.fun
new file mode 100644
index 0000000..94783c7
--- /dev/null
+++ b/examples/math_floor.fun
@@ -0,0 +1,36 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+// Demo of C99-like floor(x)
+
+print("=== math floor demo start ===")
+
+print("floor(3.7) -> " + to_string(floor(3.7)))     // 3
+print("floor(3.0) -> " + to_string(floor(3.0)))     // 3
+print("floor(-3.2) -> " + to_string(floor(-3.2)))   // -4
+print("floor(-3.0) -> " + to_string(floor(-3.0)))   // -3
+print("floor(0.5) -> " + to_string(floor(0.5)))     // 0
+print("floor(-0.5) -> " + to_string(floor(-0.5)))   // -1
+
+print("=== math floor demo end ===")
+
+/* Expected output (values):
+=== math floor demo start ===
+floor(3.7) -> 3
+floor(3.0) -> 3
+floor(-3.2) -> -4
+floor(-3.0) -> -3
+floor(0.5) -> 0
+floor(-0.5) -> -1
+=== math floor demo end ===
+*/
diff --git a/examples/math_round.fun b/examples/math_round.fun
new file mode 100644
index 0000000..0c2117c
--- /dev/null
+++ b/examples/math_round.fun
@@ -0,0 +1,36 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+// Demo of C99-like round(x) — half away from zero
+
+print("=== math round demo start ===")
+
+print("round(3.2) -> " + to_string(round(3.2)))     // 3
+print("round(3.5) -> " + to_string(round(3.5)))     // 4
+print("round(3.8) -> " + to_string(round(3.8)))     // 4
+print("round(-3.2) -> " + to_string(round(-3.2)))   // -3
+print("round(-3.5) -> " + to_string(round(-3.5)))   // -4
+print("round(-3.8) -> " + to_string(round(-3.8)))   // -4
+
+print("=== math round demo end ===")
+
+/* Expected output (values):
+=== math round demo start ===
+round(3.2) -> 3
+round(3.5) -> 4
+round(3.8) -> 4
+round(-3.2) -> -3
+round(-3.5) -> -4
+round(-3.8) -> -4
+=== math round demo end ===
+*/
diff --git a/examples/math_trunc.fun b/examples/math_trunc.fun
new file mode 100644
index 0000000..e8f395b
--- /dev/null
+++ b/examples/math_trunc.fun
@@ -0,0 +1,36 @@
+#!/usr/bin/env fun
+
+/*
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+// Demo of C99-like trunc(x) — rounds toward zero
+
+print("=== math trunc demo start ===")
+
+print("trunc(3.7) -> " + to_string(trunc(3.7)))     // 3
+print("trunc(3.0) -> " + to_string(trunc(3.0)))     // 3
+print("trunc(-3.7) -> " + to_string(trunc(-3.7)))   // -3
+print("trunc(-3.0) -> " + to_string(trunc(-3.0)))   // -3
+print("trunc(0.5) -> " + to_string(trunc(0.5)))     // 0
+print("trunc(-0.5) -> " + to_string(trunc(-0.5)))   // 0
+
+print("=== math trunc demo end ===")
+
+/* Expected output (values):
+=== math trunc demo start ===
+trunc(3.7) -> 3
+trunc(3.0) -> 3
+trunc(-3.7) -> -3
+trunc(-3.0) -> -3
+trunc(0.5) -> 0
+trunc(-0.5) -> 0
+=== math trunc demo end ===
+*/
diff --git a/src/bytecode.c b/src/bytecode.c
index f1af0e2..05bdcec 100644
--- a/src/bytecode.c
+++ b/src/bytecode.c
@@ -189,6 +189,10 @@ static const char *opcode_name(OpCode op) {
         case OP_TK_LABEL: return "TK_LABEL";
         case OP_TK_BUTTON: return "TK_BUTTON";
         case OP_TK_PACK: return "TK_PACK";
+        case OP_FLOOR: return "FLOOR";
+        case OP_CEIL: return "CEIL";
+        case OP_TRUNC: return "TRUNC";
+        case OP_ROUND: return "ROUND";
         default: return "???";
     }
 }
diff --git a/src/bytecode.h b/src/bytecode.h
index 0c0e971..2d29b40 100644
--- a/src/bytecode.h
+++ b/src/bytecode.h
@@ -236,7 +236,13 @@ typedef enum {
     // exceptions (minimal)
     OP_TRY_PUSH,           // operand = handler ip; push handler onto try-stack
     OP_TRY_POP,            // pop current handler
-    OP_THROW               // pops error value; if handler -> jump to it (push err), else print and terminate
+    OP_THROW,              // pops error value; if handler -> jump to it (push err), else print and terminate
+
+    // C99 math.h rounding family (float-aware)
+    OP_FLOOR,             // pops x (int/float); pushes floor(x) (int if integral else float)
+    OP_CEIL,              // pops x (int/float); pushes ceil(x)  (int if integral else float)
+    OP_TRUNC,             // pops x (int/float); pushes trunc(x) (int if integral else float)
+    OP_ROUND              // pops x (int/float); pushes round(x) (half away from zero)
 } OpCode;
 
 typedef struct {
diff --git a/src/fun_test.c b/src/fun_test.c
index 64928f8..f71f8a1 100644
--- a/src/fun_test.c
+++ b/src/fun_test.c
@@ -33,6 +33,12 @@ int main(void) {
     int c3 = bytecode_add_constant(bc, make_int(3));
     int c10 = bytecode_add_constant(bc, make_int(10));
     int c42 = bytecode_add_constant(bc, make_int(42));
+    int cf3_2 = bytecode_add_constant(bc, make_float(3.2));
+    int cf3_5 = bytecode_add_constant(bc, make_float(3.5));
+    int cf3_8 = bytecode_add_constant(bc, make_float(3.8));
+    int cfn3_2 = bytecode_add_constant(bc, make_float(-3.2));
+    int cfn3_5 = bytecode_add_constant(bc, make_float(-3.5));
+    int cfn3_8 = bytecode_add_constant(bc, make_float(-3.8));
 
     // ---------- Arithmetic ----------
     bytecode_add_instruction(bc, OP_LOAD_CONST, c42);
@@ -120,6 +126,48 @@ int main(void) {
     bytecode_add_instruction(bc, OP_LOAD_CONST, c1);
     bytecode_add_instruction(bc, OP_POP, 0);        // dApache-2.0ard 1 (stack now empty)
 
+    // ---------- Rounding (math.h) demo ----------
+    // floor/ceil/trunc/round on representative values
+    int start_round_demo = bc->instr_count;
+    (void)start_round_demo;
+
+    // +3.2
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cf3_2);
+    bytecode_add_instruction(bc, OP_FLOOR, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cf3_2);
+    bytecode_add_instruction(bc, OP_CEIL, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cf3_2);
+    bytecode_add_instruction(bc, OP_TRUNC, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cf3_2);
+    bytecode_add_instruction(bc, OP_ROUND, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+
+    // +3.5
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cf3_5);
+    bytecode_add_instruction(bc, OP_ROUND, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+
+    // -3.5
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cfn3_5);
+    bytecode_add_instruction(bc, OP_ROUND, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+
+    // -3.2
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cfn3_2);
+    bytecode_add_instruction(bc, OP_FLOOR, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+    bytecode_add_instruction(bc, OP_LOAD_CONST, cfn3_2);
+    bytecode_add_instruction(bc, OP_CEIL, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+
+    // integers should be unchanged
+    bytecode_add_instruction(bc, OP_LOAD_CONST, c10);
+    bytecode_add_instruction(bc, OP_FLOOR, 0);
+    bytecode_add_instruction(bc, OP_PRINT, 0);
+
     // ---------- HALT ----------
     bytecode_add_instruction(bc, OP_HALT, 0);
 
diff --git a/src/parser.c b/src/parser.c
index 67a4599..fb243c5 100644
--- a/src/parser.c
+++ b/src/parser.c
@@ -1758,6 +1758,34 @@ static int emit_primary(Bytecode *bc, const char *src, size_t len, size_t *pos)
                 free(name);
                 return 1;
             }
+            if (strcmp(name, "floor") == 0) {
+                (*pos)++; /* '(' */
+                if (!emit_expression(bc, src, len, pos) || !consume_char(src, len, pos, ')')) { parser_fail(*pos, "floor expects 1 arg"); free(name); return 0; }
+                bytecode_add_instruction(bc, OP_FLOOR, 0);
+                free(name);
+                return 1;
+            }
+            if (strcmp(name, "ceil") == 0) {
+                (*pos)++; /* '(' */
+                if (!emit_expression(bc, src, len, pos) || !consume_char(src, len, pos, ')')) { parser_fail(*pos, "ceil expects 1 arg"); free(name); return 0; }
+                bytecode_add_instruction(bc, OP_CEIL, 0);
+                free(name);
+                return 1;
+            }
+            if (strcmp(name, "trunc") == 0) {
+                (*pos)++; /* '(' */
+                if (!emit_expression(bc, src, len, pos) || !consume_char(src, len, pos, ')')) { parser_fail(*pos, "trunc expects 1 arg"); free(name); return 0; }
+                bytecode_add_instruction(bc, OP_TRUNC, 0);
+                free(name);
+                return 1;
+            }
+            if (strcmp(name, "round") == 0) {
+                (*pos)++; /* '(' */
+                if (!emit_expression(bc, src, len, pos) || !consume_char(src, len, pos, ')')) { parser_fail(*pos, "round expects 1 arg"); free(name); return 0; }
+                bytecode_add_instruction(bc, OP_ROUND, 0);
+                free(name);
+                return 1;
+            }
             if (strcmp(name, "pow") == 0) {
                 (*pos)++; /* '(' */
                 if (!emit_expression(bc, src, len, pos) || !consume_char(src, len, pos, ',')) { parser_fail(*pos, "pow expects 2 args"); free(name); return 0; }
diff --git a/src/vm.c b/src/vm.c
index e67aef5..951ab9d 100644
--- a/src/vm.c
+++ b/src/vm.c
@@ -674,6 +674,10 @@ void vm_run(VM *vm, Bytecode *entry) {
             #include "vm/math/min.c"
             #include "vm/math/mod.c"
             #include "vm/math/pow.c"
+            #include "vm/math/floor.c"
+            #include "vm/math/ceil.c"
+            #include "vm/math/trunc.c"
+            #include "vm/math/round.c"
             #include "vm/math/random_int.c"
             #include "vm/math/random_seed.c"
 
diff --git a/src/vm/math/ceil.c b/src/vm/math/ceil.c
new file mode 100644
index 0000000..bda8d29
--- /dev/null
+++ b/src/vm/math/ceil.c
@@ -0,0 +1,43 @@
+/**
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+/**
+* @file ceil.c
+ * @brief Implements the OP_CEIL opcode using C99 math.h ceil().
+ */
+
+#include <math.h>
+
+case OP_CEIL: {
+    Value v = pop_value(vm);
+    if (v.type == VAL_INT) {
+        /* ceil(n) == n for integers */
+        push_value(vm, make_int(v.i));
+        free_value(v);
+    } else if (v.type == VAL_FLOAT) {
+        double r = ceil(v.d);
+        if (r >= (double)INT64_MIN && r <= (double)INT64_MAX) {
+            int64_t ii = (int64_t)r;
+            if ((double)ii == r) {
+                push_value(vm, make_int(ii));
+            } else {
+                push_value(vm, make_float(r));
+            }
+        } else {
+            push_value(vm, make_float(r));
+        }
+        free_value(v);
+    } else {
+        fprintf(stderr, "Runtime type error: CEIL expects number, got %s\n", value_type_name(v.type));
+        exit(1);
+    }
+    break;
+}
diff --git a/src/vm/math/floor.c b/src/vm/math/floor.c
new file mode 100644
index 0000000..72e2440
--- /dev/null
+++ b/src/vm/math/floor.c
@@ -0,0 +1,43 @@
+/**
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+/**
+* @file floor.c
+ * @brief Implements the OP_FLOOR opcode using C99 math.h floor().
+ */
+
+#include <math.h>
+
+case OP_FLOOR: {
+    Value v = pop_value(vm);
+    if (v.type == VAL_INT) {
+        /* floor(n) == n for integers */
+        push_value(vm, make_int(v.i));
+        free_value(v);
+    } else if (v.type == VAL_FLOAT) {
+        double r = floor(v.d);
+        if (r >= (double)INT64_MIN && r <= (double)INT64_MAX) {
+            int64_t ii = (int64_t)r;
+            if ((double)ii == r) {
+                push_value(vm, make_int(ii));
+            } else {
+                push_value(vm, make_float(r));
+            }
+        } else {
+            push_value(vm, make_float(r));
+        }
+        free_value(v);
+    } else {
+        fprintf(stderr, "Runtime type error: FLOOR expects number, got %s\n", value_type_name(v.type));
+        exit(1);
+    }
+    break;
+}
diff --git a/src/vm/math/round.c b/src/vm/math/round.c
new file mode 100644
index 0000000..3f830ff
--- /dev/null
+++ b/src/vm/math/round.c
@@ -0,0 +1,43 @@
+/**
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ *  Added: 2026-01-03
+ */
+
+/**
+* @file round.c
+ * @brief Implements the OP_ROUND opcode using C99 math.h round().
+ *        C99 round() rounds half away from zero.
+ */
+
+#include <math.h>
+
+case OP_ROUND: {
+    Value v = pop_value(vm);
+    if (v.type == VAL_INT) {
+        push_value(vm, make_int(v.i));
+        free_value(v);
+    } else if (v.type == VAL_FLOAT) {
+        double r = round(v.d);
+        if (r >= (double)INT64_MIN && r <= (double)INT64_MAX) {
+            int64_t ii = (int64_t)r;
+            if ((double)ii == r) {
+                push_value(vm, make_int(ii));
+            } else {
+                push_value(vm, make_float(r));
+            }
+        } else {
+            push_value(vm, make_float(r));
+        }
+        free_value(v);
+    } else {
+        fprintf(stderr, "Runtime type error: ROUND expects number, got %s\n", value_type_name(v.type));
+        exit(1);
+    }
+    break;
+}
diff --git a/src/vm/math/trunc.c b/src/vm/math/trunc.c
new file mode 100644
index 0000000..7442074
--- /dev/null
+++ b/src/vm/math/trunc.c
@@ -0,0 +1,42 @@
+/**
+ * This file is part of the Fun programming language.
+ * https://fun-lang.xyz/
+ *
+ * Copyright 2026 Johannes Findeisen <you@hanez.org>
+ * Licensed under the terms of the Apache-2.0 license.
+ * https://opensource.org/license/apache-2-0
+ *
+ * Added: 2026-01-03
+ */
+
+/**
+* @file trunc.c
+ * @brief Implements the OP_TRUNC opcode using C99 math.h trunc().
+ */
+
+#include <math.h>
+
+case OP_TRUNC: {
+    Value v = pop_value(vm);
+    if (v.type == VAL_INT) {
+        push_value(vm, make_int(v.i));
+        free_value(v);
+    } else if (v.type == VAL_FLOAT) {
+        double r = trunc(v.d);
+        if (r >= (double)INT64_MIN && r <= (double)INT64_MAX) {
+            int64_t ii = (int64_t)r;
+            if ((double)ii == r) {
+                push_value(vm, make_int(ii));
+            } else {
+                push_value(vm, make_float(r));
+            }
+        } else {
+            push_value(vm, make_float(r));
+        }
+        free_value(v);
+    } else {
+        fprintf(stderr, "Runtime type error: TRUNC expects number, got %s\n", value_type_name(v.type));
+        exit(1);
+    }
+    break;
+}