diff --git a/Makefile b/Makefile
index 7e3d724..e2c9615 100644
--- a/Makefile
+++ b/Makefile
@@ -7,7 +7,7 @@ SRCS	= picoc.c table.c lex.c parse.c expression.c heap.c type.c \
 	variable.c clibrary.c platform.c include.c \
 	platform/platform_unix.c platform/library_unix.c \
 	cstdlib/stdio.c cstdlib/math.c cstdlib/string.c cstdlib/stdlib.c \
-	cstdlib/time.c cstdlib/errno.c
+	cstdlib/time.c cstdlib/errno.c cstdlib/ctype.c
 OBJS	:= $(SRCS:%.c=%.o)
 
 all: depend $(TARGET)
diff --git a/cstdlib/ctype.c b/cstdlib/ctype.c
new file mode 100644
index 0000000..d51d208
--- /dev/null
+++ b/cstdlib/ctype.c
@@ -0,0 +1,109 @@
+/* string.h library for large systems - small embedded systems use clibrary.c instead */
+#include <ctype.h>
+#include "../picoc.h"
+
+#ifndef BUILTIN_MINI_STDLIB
+
+void StdIsalnum(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isalnum(Param[0]->Val->Integer);
+}
+
+void StdIsalpha(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isalpha(Param[0]->Val->Integer);
+}
+
+void StdIsblank(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isblank(Param[0]->Val->Integer);
+}
+
+void StdIscntrl(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = iscntrl(Param[0]->Val->Integer);
+}
+
+void StdIsdigit(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isdigit(Param[0]->Val->Integer);
+}
+
+void StdIsgraph(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isgraph(Param[0]->Val->Integer);
+}
+
+void StdIslower(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = islower(Param[0]->Val->Integer);
+}
+
+void StdIsprint(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isprint(Param[0]->Val->Integer);
+}
+
+void StdIspunct(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = ispunct(Param[0]->Val->Integer);
+}
+
+void StdIsspace(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isspace(Param[0]->Val->Integer);
+}
+
+void StdIsupper(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isupper(Param[0]->Val->Integer);
+}
+
+void StdIsxdigit(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isxdigit(Param[0]->Val->Integer);
+}
+
+void StdTolower(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = tolower(Param[0]->Val->Integer);
+}
+
+void StdToupper(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = toupper(Param[0]->Val->Integer);
+}
+
+void StdIsascii(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = isascii(Param[0]->Val->Integer);
+}
+
+void StdToascii(struct ParseState *Parser, struct Value *ReturnValue, struct Value **Param, int NumArgs)
+{
+    ReturnValue->Val->Integer = toascii(Param[0]->Val->Integer);
+}
+
+/* all string.h functions */
+struct LibraryFunction StdCtypeFunctions[] =
+{
+    { StdIsalnum,      "int isalnum(int);" },
+    { StdIsalpha,      "int isalpha(int);" },
+    { StdIsblank,      "int isblank(int);" },
+    { StdIscntrl,      "int iscntrl(int);" },
+    { StdIsdigit,      "int isdigit(int);" },
+    { StdIsgraph,      "int isgraph(int);" },
+    { StdIslower,      "int islower(int);" },
+    { StdIsprint,      "int isprint(int);" },
+    { StdIspunct,      "int ispunct(int);" },
+    { StdIsspace,      "int isspace(int);" },
+    { StdIsupper,      "int isupper(int);" },
+    { StdIsxdigit,     "int isxdigit(int);" },
+    { StdTolower,      "int tolower(int);" },
+    { StdToupper,      "int toupper(int);" },
+    { StdIsascii,      "int isascii(int);" },
+    { StdToascii,      "int toascii(int);" },
+    { NULL,             NULL }
+};
+
+#endif /* !BUILTIN_MINI_STDLIB */
diff --git a/include.c b/include.c
index 7e32e93..c47144d 100644
--- a/include.c
+++ b/include.c
@@ -18,6 +18,7 @@ struct IncludeLibrary *IncludeLibList = NULL;
 /* initialise the built-in include libraries */
 void IncludeInit()
 {
+    IncludeRegister("ctype.h", NULL, &StdCtypeFunctions, NULL);
     IncludeRegister("errno.h", &StdErrnoSetupFunc, NULL, NULL);
     IncludeRegister("stdio.h", &StdioSetupFunc, &StdioFunctions, StdioDefs);
     IncludeRegister("math.h", &MathSetupFunc, &MathFunctions, NULL);
diff --git a/picoc.h b/picoc.h
index ec34f48..0b0298d 100644
--- a/picoc.h
+++ b/picoc.h
@@ -439,4 +439,7 @@ void StdTimeSetupFunc(void);
 /* errno.c */
 void StdErrnoSetupFunc(void);
 
+/* ctype.c */
+extern struct LibraryFunction StdCtypeFunctions[];
+
 #endif /* PICOC_H */