diff --git a/vlib/hash/wyhash.c.v b/vlib/hash/wyhash.c.v
index 6758321acf..4671ae2bcd 100644
--- a/vlib/hash/wyhash.c.v
+++ b/vlib/hash/wyhash.c.v
@@ -7,7 +7,7 @@ fn C.wyhash64(u64, u64) u64
 
 [inline]
 pub fn wyhash_c(key byteptr, len u64, seed u64) u64 {
-	return C.wyhash(key, len, seed, C._wyp)
+	return C.wyhash(key, len, seed, &u64(C._wyp))
 }
 
 [inline]
diff --git a/vlib/picohttpparser/request.v b/vlib/picohttpparser/request.v
index 48523d40f3..c3bbf8e1c9 100644
--- a/vlib/picohttpparser/request.v
+++ b/vlib/picohttpparser/request.v
@@ -11,10 +11,10 @@ pub mut:
 
 [inline]
 pub fn (mut r Request) parse_request(s string, max_headers int) int {
-	method_len := u64(0)
-	path_len := u64(0)
+	method_len := size_t(0)
+	path_len := size_t(0)
 	minor_version := 0
-	num_headers := u64(max_headers)
+	num_headers := size_t(max_headers)
 
 	pret := C.phr_parse_request(s.str, s.len, PPchar(&r.method.str), &method_len, PPchar(&r.path.str),
 		&path_len, &minor_version, &r.headers[0], &num_headers, 0)
@@ -23,15 +23,15 @@ pub fn (mut r Request) parse_request(s string, max_headers int) int {
 			r.method = tos(r.method.str, int(method_len))
 			r.path = tos(r.path.str, int(path_len))
 		}
-		r.num_headers = num_headers
+		r.num_headers = u64(num_headers)
 	}
 	return pret
 }
 
 [inline]
 pub fn (mut r Request) parse_request_path(s string) int {
-	method_len := u64(0)
-	path_len := u64(0)
+	method_len := size_t(0)
+	path_len := size_t(0)
 
 	pret := C.phr_parse_request_path(s.str, s.len, PPchar(&r.method.str), &method_len,
 		PPchar(&r.path.str), &path_len)
@@ -46,8 +46,8 @@ pub fn (mut r Request) parse_request_path(s string) int {
 
 [inline]
 pub fn (mut r Request) parse_request_path_pipeline(s string) int {
-	method_len := u64(0)
-	path_len := u64(0)
+	method_len := size_t(0)
+	path_len := size_t(0)
 
 	pret := C.phr_parse_request_path_pipeline(s.str, s.len, PPchar(&r.method.str), &method_len,
 		PPchar(&r.path.str), &path_len)
diff --git a/vlib/szip/szip.v b/vlib/szip/szip.v
index 53f42314c2..91beee0046 100644
--- a/vlib/szip/szip.v
+++ b/vlib/szip/szip.v
@@ -11,15 +11,15 @@ struct C.zip_t {
 
 type Zip = C.zip_t
 
-fn C.zip_open(byteptr, int, byte) &Zip
+fn C.zip_open(&char, int, char) &Zip
 
 fn C.zip_close(&Zip)
 
-fn C.zip_entry_open(&Zip, byteptr) int
+fn C.zip_entry_open(&Zip, &byte) int
 
 fn C.zip_entry_close(&Zip) int
 
-fn C.zip_entry_name(&Zip) byteptr
+fn C.zip_entry_name(&Zip) &byte
 
 fn C.zip_entry_index(&Zip) int
 
@@ -29,17 +29,17 @@ fn C.zip_entry_size(&Zip) u64
 
 fn C.zip_entry_crc32(&Zip) u32
 
-fn C.zip_entry_write(&Zip, voidptr, int) int
+fn C.zip_entry_write(&Zip, voidptr, size_t) int
 
-fn C.zip_entry_fwrite(&Zip, byteptr) int
+fn C.zip_entry_fwrite(&Zip, &char) int
 
-fn C.zip_entry_read(&Zip, byteptr, int) int
+fn C.zip_entry_read(&Zip, &&byte, &size_t) int
 
-fn C.zip_entry_fread(&Zip, byteptr) int
+fn C.zip_entry_fread(&Zip, &char) int
 
 fn C.zip_total_entries(&Zip) int
 
-fn C.zip_extract_without_callback(charptr, charptr) int
+fn C.zip_extract_without_callback(&char, &char) int
 
 // CompressionLevel lists compression levels, see in "thirdparty/zip/miniz.h"
 pub enum CompressionLevel {
@@ -84,7 +84,7 @@ pub fn open(name string, level CompressionLevel, mode OpenMode) ?&Zip {
 	if name.len == 0 {
 		return error('szip: name of file empty')
 	}
-	p_zip := &Zip(C.zip_open(name.str, int(level), mode.to_byte()))
+	p_zip := &Zip(C.zip_open(name.str, int(level), char(mode.to_byte())))
 	if isnil(p_zip) {
 		return error('szip: cannot open/create/append new zip archive')
 	}
@@ -183,8 +183,8 @@ pub fn (mut zentry Zip) create_entry(name string) ? {
 // NOTE: remember to release the memory allocated for an output buffer.
 // for large entries, please take a look at zip_entry_extract function.
 pub fn (mut zentry Zip) read_entry() ?voidptr {
-	mut buf := voidptr(0)
-	mut bsize := i64(0)
+	mut buf := &byte(0)
+	mut bsize := size_t(0)
 	res := C.zip_entry_read(zentry, &buf, &bsize)
 	if res == -1 {
 		return error('szip: cannot read properly data from entry')
diff --git a/vlib/time/time_nix.c.v b/vlib/time/time_nix.c.v
index 1179519eb7..76ccc1a042 100644
--- a/vlib/time/time_nix.c.v
+++ b/vlib/time/time_nix.c.v
@@ -79,7 +79,7 @@ fn linux_now() Time {
 	mut ts := C.timespec{}
 	C.clock_gettime(C.CLOCK_REALTIME, &ts)
 	loc_tm := C.tm{}
-	C.localtime_r(&ts.tv_sec, &loc_tm)
+	C.localtime_r(&time.time_t(&ts.tv_sec), &loc_tm)
 	return convert_ctime(loc_tm, int(ts.tv_nsec / 1000))
 }
 
diff --git a/vlib/v/ast/types.v b/vlib/v/ast/types.v
index cb80244b7c..f82d467d9c 100644
--- a/vlib/v/ast/types.v
+++ b/vlib/v/ast/types.v
@@ -283,7 +283,7 @@ pub fn (typ Type) is_float() bool {
 
 [inline]
 pub fn (typ Type) is_int() bool {
-	return typ.idx() in ast.integer_type_idxs
+	return int(typ) in ast.integer_type_idxs
 }
 
 [inline]
@@ -298,12 +298,12 @@ pub fn (typ Type) is_unsigned() bool {
 
 [inline]
 pub fn (typ Type) is_int_literal() bool {
-	return typ.idx() == ast.int_literal_type_idx
+	return int(typ) == ast.int_literal_type_idx
 }
 
 [inline]
 pub fn (typ Type) is_number() bool {
-	return typ.idx() in ast.number_type_idxs
+	return int(typ) in ast.number_type_idxs
 }
 
 [inline]
diff --git a/vlib/v/checker/check_types.v b/vlib/v/checker/check_types.v
index 8aad2cac64..43826c4ff4 100644
--- a/vlib/v/checker/check_types.v
+++ b/vlib/v/checker/check_types.v
@@ -139,6 +139,15 @@ pub fn (mut c Checker) check_basic(got ast.Type, expected ast.Type) bool {
 	if got == ast.error_type_idx && expected == ast.string_type_idx {
 		return true
 	}
+	// allow `return 0` in a function with `?int` return type
+	expected_nonopt := expected.clear_flag(.optional)
+	if got == ast.int_literal_type && expected_nonopt.is_int() {
+		return true
+	}
+	// allow `return 0` in a function with `?f32` return type
+	if got == ast.float_literal_type && expected_nonopt.is_float() {
+		return true
+	}
 	return false
 }
 
diff --git a/vlib/v/checker/checker.v b/vlib/v/checker/checker.v
index b7093aae36..c4086cd39b 100644
--- a/vlib/v/checker/checker.v
+++ b/vlib/v/checker/checker.v
@@ -1096,6 +1096,10 @@ pub fn (mut c Checker) infix_expr(mut infix_expr ast.InfixExpr) ast.Type {
 		if left_type == ast.void_type || right_type == ast.void_type {
 			return ast.void_type
 		}
+		if left_type.nr_muls() > 0 && right_type.is_int() {
+			// pointer arithmetic is fine, it is checked in other places
+			return return_type
+		}
 		c.error('infix expr: cannot use `$right.name` (right expression) as `$left.name`',
 			left_right_pos)
 	}
diff --git a/vlib/v/gen/c/cgen.v b/vlib/v/gen/c/cgen.v
index 9400f78e83..14f2649268 100644
--- a/vlib/v/gen/c/cgen.v
+++ b/vlib/v/gen/c/cgen.v
@@ -3180,7 +3180,7 @@ fn (mut g Gen) typeof_expr(node ast.TypeOf) {
 		varg_elem_type_sym := g.table.get_type_symbol(g.table.value_type(node.expr_type))
 		g.write('_SLIT("...${util.strip_main_name(varg_elem_type_sym.name)}")')
 	} else {
-		g.write('_SLIT("${util.strip_main_name(sym.name)}")')
+		g.write('_SLIT("${util.strip_main_name(g.table.type_to_str(node.expr_type))}")')
 	}
 }