diff --git a/compiler/table.v b/compiler/table.v
index fa8bdd35ec..2211f10324 100644
--- a/compiler/table.v
+++ b/compiler/table.v
@@ -210,6 +210,7 @@ fn new_table(obfuscate bool) &Table {
 	t.register_type('size_t')
 	t.register_type_with_parent('i8', 'int')
 	t.register_type_with_parent('byte', 'int')
+	t.register_type_with_parent('char', 'int') // for C functinos only, to avoid warnings
 	t.register_type_with_parent('i16', 'int')
 	t.register_type_with_parent('u16', 'u32')
 	t.register_type_with_parent('u32', 'int')
diff --git a/vlib/builtin/array.v b/vlib/builtin/array.v
index 133e1ce0a3..834cb3c8b0 100644
--- a/vlib/builtin/array.v
+++ b/vlib/builtin/array.v
@@ -276,7 +276,7 @@ pub fn (b []byte) hex() string {
 	mut hex := malloc(b.len*2+1)
 	mut ptr := &hex[0]
 	for i := 0; i < b.len ; i++ {
-		ptr += C.sprintf(ptr, '%02x', b[i])
+		ptr += C.sprintf(*char(ptr), '%02x', b[i])
 	}
 	return string(hex)
 }
diff --git a/vlib/builtin/string.v b/vlib/builtin/string.v
index 08c63f9601..76e2a48f16 100644
--- a/vlib/builtin/string.v
+++ b/vlib/builtin/string.v
@@ -128,28 +128,28 @@ pub fn (s string) replace(rep, with string) string {
 }
 
 pub fn (s string) int() int {
-	return C.atoi(s.str)
+	return C.atoi(*char(s.str))
 }
 
 
 pub fn (s string) i64() i64 {
-	return C.atoll(s.str)
+	return C.atoll(*char(s.str))
 }
 
 pub fn (s string) f32() f32 {
-	return C.atof(s.str)
+	return C.atof(*char(s.str))
 }
 
 pub fn (s string) f64() f64 {
-	return C.atof(s.str)
+	return C.atof(*char(s.str))
 }
 
 pub fn (s string) u32() u32 {
-	return C.strtoul(s.str, 0, 0)
+	return C.strtoul(*char(s.str), 0, 0)
 }
 
 pub fn (s string) u64() u64 {
-	return C.strtoull(s.str, 0, 0)
+	return C.strtoull(*char(s.str), 0, 0)
 	//return C.atoll(s.str) // temporary fix for tcc on windows.
 }