diff --git a/reactos/lib/crtdll/mbstring/islwr.c b/reactos/lib/crtdll/mbstring/islwr.c
index 861206c5610..f64eade4c06 100644
--- a/reactos/lib/crtdll/mbstring/islwr.c
+++ b/reactos/lib/crtdll/mbstring/islwr.c
@@ -18,6 +18,6 @@ int _ismbclower( unsigned int c )
 		if ( c >= 0x829A && c<= 0x829A )
 			return 1;
 	}
-	else
-		return isupper(c);
+
+	return islower(c);
 }
diff --git a/reactos/lib/crtdll/mbstring/ismbal.c b/reactos/lib/crtdll/mbstring/ismbal.c
index 736b67edf33..9a6d52283cc 100644
--- a/reactos/lib/crtdll/mbstring/ismbal.c
+++ b/reactos/lib/crtdll/mbstring/ismbal.c
@@ -10,6 +10,8 @@
 #include <crtdll/mbctype.h>
 #include <crtdll/ctype.h>
 
+int _ismbbkalnum( unsigned int c );
+
 int _ismbbalpha(unsigned char c)
 {
 	return (isalpha(c) ||_ismbbkalnum(c));
diff --git a/reactos/lib/crtdll/mbstring/ismbaln.c b/reactos/lib/crtdll/mbstring/ismbaln.c
index 78a39992eca..4ba416d5d42 100644
--- a/reactos/lib/crtdll/mbstring/ismbaln.c
+++ b/reactos/lib/crtdll/mbstring/ismbaln.c
@@ -1,4 +1,7 @@
 #include <crtdll/mbctype.h>
+#include <crtdll/ctype.h>
+
+int _ismbbkalnum( unsigned int c );
 
 int _ismbbalnum(unsigned char c)
 {
diff --git a/reactos/lib/crtdll/mbstring/ismbc.c b/reactos/lib/crtdll/mbstring/ismbc.c
index b69dd90c4bc..2747a5a5ae2 100644
--- a/reactos/lib/crtdll/mbstring/ismbc.c
+++ b/reactos/lib/crtdll/mbstring/ismbc.c
@@ -1,5 +1,8 @@
 #include <crtdll/mbstring.h>
 
+int _ismbbalpha(unsigned char c);
+int _ismbbalnum(unsigned char c);
+
 int _ismbcalnum( unsigned int c )
 {
 	if ((c & 0xFF00) != 0) {
@@ -11,7 +14,7 @@ int _ismbcalnum( unsigned int c )
 
 	return 0;
 }
-  
+
 int _ismbcalpha( unsigned int c )
 {
 	if ((c & 0xFF00) != 0) {
diff --git a/reactos/lib/crtdll/mbstring/ismbkaln.c b/reactos/lib/crtdll/mbstring/ismbkaln.c
index 514c0233e2c..26f53c948f9 100644
--- a/reactos/lib/crtdll/mbstring/ismbkaln.c
+++ b/reactos/lib/crtdll/mbstring/ismbkaln.c
@@ -8,6 +8,7 @@
  *              12/04/99: Created
  */
 #include <crtdll/mbctype.h>
+#include <crtdll/ctype.h>
 
 int _ismbbkalnum( unsigned int c )
 {
diff --git a/reactos/lib/crtdll/mbstring/ismblead.c b/reactos/lib/crtdll/mbstring/ismblead.c
index b4e3ae654b3..92822101d10 100644
--- a/reactos/lib/crtdll/mbstring/ismblead.c
+++ b/reactos/lib/crtdll/mbstring/ismblead.c
@@ -13,6 +13,7 @@
 #include <crtdll/stdlib.h>
 #include <crtdll/mbctype.h>
 
+size_t _mbclen2(const unsigned int s);
 
 char _jctype[257] = {
 /*-1*/  ___,
diff --git a/reactos/lib/crtdll/mbstring/ismbtrl.c b/reactos/lib/crtdll/mbstring/ismbtrl.c
index 1fb5fd9bbd6..8d37b422846 100644
--- a/reactos/lib/crtdll/mbstring/ismbtrl.c
+++ b/reactos/lib/crtdll/mbstring/ismbtrl.c
@@ -11,6 +11,8 @@
 #include <crtdll/mbstring.h>
 #include <crtdll/mbctype.h>
 
+size_t _mbclen2(const unsigned int s);
+
 //  iskanji2()   : (0x40 <= c <= 0x7E 0x80  <=  c <= 0xFC) 
 
 int _ismbbtrail(unsigned int c)
diff --git a/reactos/lib/crtdll/mbstring/isuppr.c b/reactos/lib/crtdll/mbstring/isuppr.c
index 47e0ebe1ded..05afc644eaa 100644
--- a/reactos/lib/crtdll/mbstring/isuppr.c
+++ b/reactos/lib/crtdll/mbstring/isuppr.c
@@ -18,6 +18,6 @@ int _ismbcupper( unsigned int c )
 		if ( c >= 0x8260 && c<= 0x8279 )
 			return 1;
 	}
-	else
-		return isupper(c);
+
+	return isupper(c);
 }
diff --git a/reactos/lib/crtdll/mbstring/mbccpy.c b/reactos/lib/crtdll/mbstring/mbccpy.c
index 8e2e46e9e17..65dbd044c92 100644
--- a/reactos/lib/crtdll/mbstring/mbccpy.c
+++ b/reactos/lib/crtdll/mbstring/mbccpy.c
@@ -1,4 +1,7 @@
 #include <crtdll/mbstring.h>
+#include <crtdll/string.h>
+
+size_t _mbclen2(const unsigned int s);
 
 void _mbccpy(unsigned char *dst, const unsigned char *src)
 {
diff --git a/reactos/lib/crtdll/mbstring/mbscat.c b/reactos/lib/crtdll/mbstring/mbscat.c
index c7461d9b65f..bed2d66ed92 100644
--- a/reactos/lib/crtdll/mbstring/mbscat.c
+++ b/reactos/lib/crtdll/mbstring/mbscat.c
@@ -1,3 +1,5 @@
+#include <crtdll/string.h>
+
 unsigned char * _mbscat(unsigned char *dst, const unsigned char *src)
 {
 	return strcat(dst,src);
diff --git a/reactos/lib/crtdll/mbstring/mbschr.c b/reactos/lib/crtdll/mbstring/mbschr.c
index caf9b969146..5efab5df26e 100644
--- a/reactos/lib/crtdll/mbstring/mbschr.c
+++ b/reactos/lib/crtdll/mbstring/mbschr.c
@@ -1,3 +1,5 @@
+#include <crtdll/string.h>
+
 unsigned char * _mbschr(const unsigned char *str, unsigned int c)
 {
 	return strchr(str,c);
diff --git a/reactos/lib/crtdll/mbstring/mbscmp.c b/reactos/lib/crtdll/mbstring/mbscmp.c
index 6baf040372d..1f121f0c447 100644
--- a/reactos/lib/crtdll/mbstring/mbscmp.c
+++ b/reactos/lib/crtdll/mbstring/mbscmp.c
@@ -1,4 +1,5 @@
 #include <crtdll/mbstring.h>
+#include <crtdll/string.h>
 
 int _mbscmp(const unsigned char *str1, const unsigned char *str2)
 {
diff --git a/reactos/lib/crtdll/mbstring/mbscpy.c b/reactos/lib/crtdll/mbstring/mbscpy.c
index 1d3f60621b2..035c76d8295 100644
--- a/reactos/lib/crtdll/mbstring/mbscpy.c
+++ b/reactos/lib/crtdll/mbstring/mbscpy.c
@@ -1,3 +1,5 @@
+#include <crtdll/mbstring.h>
+#include <crtdll/string.h>
 
 unsigned char * _mbscpy(unsigned char *dst, const unsigned char *str)
 {
diff --git a/reactos/lib/crtdll/mbstring/mbslen.c b/reactos/lib/crtdll/mbstring/mbslen.c
index 8648ca82221..dd58362dd21 100644
--- a/reactos/lib/crtdll/mbstring/mbslen.c
+++ b/reactos/lib/crtdll/mbstring/mbslen.c
@@ -1,5 +1,7 @@
 #include <crtdll/mbstring.h>
 
+size_t _mbclen2(const unsigned int s);
+
 size_t _mbslen(const unsigned char *str)
 {
 	int i = 0;
@@ -8,6 +10,6 @@ size_t _mbslen(const unsigned char *str)
 	if (str == 0)
 		return 0;
 		
-    	for (s = (unsigned char *)str; *s; s+=_mbclen2(*s),i++);
+	for (s = (unsigned char *)str; *s; s+=_mbclen2(*s),i++);
 	return i;
 }
\ No newline at end of file
diff --git a/reactos/lib/crtdll/mbstring/mbsncat.c b/reactos/lib/crtdll/mbstring/mbsncat.c
index 3d7e81bdb30..9cc580f9328 100644
--- a/reactos/lib/crtdll/mbstring/mbsncat.c
+++ b/reactos/lib/crtdll/mbstring/mbsncat.c
@@ -9,13 +9,15 @@
  */
 
 #include <crtdll/mbstring.h>
+#include <crtdll/string.h>
 
+size_t _mbclen2(const unsigned int s);
 
 unsigned char * _mbsncat(unsigned char *dst, const unsigned char *src, size_t n)
 {
-	char *d = (char *)dst; 
-    	char *s = (char *)src;	
-    	if (n != 0) {
+	char *d = (char *)dst;
+	char *s = (char *)src;
+	if (n != 0) {
 		d = dst + strlen(dst); // get the end of string 
 		d += _mbclen2(*d); // move 1 or 2 up
 
@@ -25,19 +27,19 @@ unsigned char * _mbsncat(unsigned char *dst, const unsigned char *src, size_t n)
 				while (--n != 0)
 					*d++ = 0;
 				break;
-      			}
+			}
 			if (!_ismbblead(*s) )
 				n--;
-    		} while (n > 0);
-  	}
-  	return dst;
+		} while (n > 0);
+	}
+	return dst;
 }
 
 unsigned char * _mbsnbcat(unsigned char *dst, const unsigned char *src, size_t n)
 {
 	char *d; 
-    	char *s = (char *)src;	
-    	if (n != 0) {
+	char *s = (char *)src;
+	if (n != 0) {
 		d = dst + strlen(dst); // get the end of string 
 		d += _mbclen2(*d); // move 1 or 2 up
 
@@ -47,10 +49,10 @@ unsigned char * _mbsnbcat(unsigned char *dst, const unsigned char *src, size_t n
 				while (--n != 0)
 					*d++ = 0;
 				break;
-      			}
+			}
 			if ( !(n==1 && _ismbblead(*s)) )
 				n--;
-    		} while (n > 0);
-  	}
-  	return dst;
-}	
\ No newline at end of file
+		} while (n > 0);
+	}
+	return dst;
+}
diff --git a/reactos/lib/crtdll/mbstring/mbsnicmp.c b/reactos/lib/crtdll/mbstring/mbsnicmp.c
index 09e6afb54eb..57d7c8ab1fa 100644
--- a/reactos/lib/crtdll/mbstring/mbsnicmp.c
+++ b/reactos/lib/crtdll/mbstring/mbsnicmp.c
@@ -1,5 +1,8 @@
 #include <crtdll/mbstring.h>
 
+size_t _mbclen2(const unsigned int s);
+unsigned int _mbbtoupper(unsigned int c);
+
 int _mbsnicmp(const unsigned char *s1, const unsigned char *s2, size_t n)
 {
   if (n == 0)
@@ -10,14 +13,14 @@ int _mbsnicmp(const unsigned char *s1, const unsigned char *s2, size_t n)
     *s1 += _mbclen2(*s1);
     *s2 += _mbclen2(*s2);
 
-
     if (*s1 == 0)
       break;
     if (!_ismbblead(*s1) )
-	n--;
+      n--;
   } while (n > 0);
   return 0;
 }
+
 int _mbsnbicmp(const unsigned char *s1, const unsigned char *s2, size_t n)
 {
   if (n == 0)
@@ -28,10 +31,9 @@ int _mbsnbicmp(const unsigned char *s1, const unsigned char *s2, size_t n)
     s1 += _mbclen2(*s1);
     s2 += _mbclen2(*s2);
 
-
     if (*s1 == 0)
       break;
     n--;
   } while (n > 0);
   return 0;
-}
\ No newline at end of file
+}
diff --git a/reactos/lib/crtdll/mbstring/mbsnset.c b/reactos/lib/crtdll/mbstring/mbsnset.c
index f4f94d60571..a30ad4d67a5 100644
--- a/reactos/lib/crtdll/mbstring/mbsnset.c
+++ b/reactos/lib/crtdll/mbstring/mbsnset.c
@@ -9,58 +9,56 @@
  */
 #include <crtdll/mbstring.h>
 
+size_t _mbclen2(const unsigned int s);
+
 unsigned char * _mbsnset(unsigned char *src, unsigned int val, size_t count)
 {
-
-	
 	unsigned char *char_src = (unsigned char *)src;
 	unsigned short *short_src = (unsigned short *)src;
-       
+
 	if ( _mbclen2(val) == 1 ) {
 	
 		while(count > 0) {
-                	*char_src = val;
-                	char_src++;
-                	count--;
-        	}
-        	*char_src = 0;
-        }
-        else {
+			*char_src = val;
+			char_src++;
+			count--;
+		}
+		*char_src = 0;
+	}
+	else {
 		while(count > 0) {
-                	*short_src = val;
-                	short_src++;
-                	count-=2;
-        	}    	
-        	*short_src = 0;
-        }
-        
-        return src;
-	
+			*short_src = val;
+			short_src++;
+			count-=2;
+		}
+		*short_src = 0;
+	}
+
+	return src;
 }
 
 unsigned char * _mbsnbset(unsigned char *src, unsigned int val, size_t count)
 {
-	
 	unsigned char *char_src = (unsigned char *)src;
 	unsigned short *short_src = (unsigned short *)src;
-       
+
 	if ( _mbclen2(val) == 1 ) {
 	
 		while(count > 0) {
-                	*char_src = val;
-                	char_src++;
-                	count--;
-        	}
-        	*char_src = 0;
-        }
-        else {
+			*char_src = val;
+			char_src++;
+			count--;
+		}
+		*char_src = 0;
+	}
+	else {
 		while(count > 0) {
-                	*short_src = val;
-                	short_src++;
-                	count-=2;
-        	}    	
-        	*short_src = 0;
-        }
-        
-        return src;
+			*short_src = val;
+			short_src++;
+			count-=2;
+		}
+		*short_src = 0;
+	}
+
+	return src;
 }
\ No newline at end of file
diff --git a/reactos/lib/crtdll/mbstring/mbsrchr.c b/reactos/lib/crtdll/mbstring/mbsrchr.c
index ee747277182..824e639b690 100644
--- a/reactos/lib/crtdll/mbstring/mbsrchr.c
+++ b/reactos/lib/crtdll/mbstring/mbsrchr.c
@@ -10,21 +10,21 @@
 
 #include <crtdll/mbstring.h>
 
+size_t _mbclen2(const unsigned int s);
+
 unsigned char * _mbsrchr(const unsigned char *src, unsigned int val)
 {
+	char  *s = (char *)src;
+	short cc = val;
+	const char *sp=(char *)0;
 
-  char  *s = src;
-  short cc = val;
-  const char *sp=(char *)0;
-
-  
-  while (*s)
-  {	
-    	if (*(short *)s == cc)
-      		sp = s;
-    	s+= _mbclen2(*s);
-  }
-  if (cc == 0)
-    	sp = s;
-  return (char *)sp;
-}
\ No newline at end of file
+	while (*s)
+	{
+		if (*(short *)s == cc)
+			sp = s;
+		s+= _mbclen2(*s);
+	}
+	if (cc == 0)
+		sp = s;
+	return (char *)sp;
+}
diff --git a/reactos/lib/crtdll/mbstring/mbsset.c b/reactos/lib/crtdll/mbstring/mbsset.c
index 5975dfaf123..e840ed43ad5 100644
--- a/reactos/lib/crtdll/mbstring/mbsset.c
+++ b/reactos/lib/crtdll/mbstring/mbsset.c
@@ -10,26 +10,28 @@
 
 #include <crtdll/mbstring.h>
 
+size_t _mbclen2(const unsigned int s);
+
 unsigned char * _mbsset(unsigned char *src, unsigned int c)
 {
 	unsigned char *char_src = src;
-	unsigned short *short_src = src;
-       
+	unsigned short *short_src = (unsigned short *)src;
+
 	if ( _mbclen2(c) == 1 ) {
 	
 		while(*char_src != 0) {
-                	*char_src = c;
-                	char_src++;
-        	}
-        	*char_src = 0;
-        }
-        else {
+			*char_src = c;
+			char_src++;
+		}
+		*char_src = 0;
+	}
+	else {
 		while(*short_src != 0) {
-                	*short_src = c;
-                	short_src++;
-        	}    	
-        	*short_src = 0;
-        }
-        
-        return src;
-}
\ No newline at end of file
+			*short_src = c;
+			short_src++;
+		}
+		*short_src = 0;
+	}
+
+	return src;
+}
diff --git a/reactos/lib/crtdll/mbstring/mbsspnp.c b/reactos/lib/crtdll/mbstring/mbsspnp.c
index b847dd08131..ee22b4feb79 100644
--- a/reactos/lib/crtdll/mbstring/mbsspnp.c
+++ b/reactos/lib/crtdll/mbstring/mbsspnp.c
@@ -10,5 +10,5 @@ unsigned char * _mbsspnp(const unsigned char *s1, const unsigned char *s2)
   for (spanp = s2; (sc = *spanp++) != 0;)
     if (sc == c)
       goto cont;
-  return p;
+  return (unsigned char *)p;
 }
\ No newline at end of file
diff --git a/reactos/lib/crtdll/mbstring/mbsstr.c b/reactos/lib/crtdll/mbstring/mbsstr.c
index bcc5b38c33a..f6c850d60f3 100644
--- a/reactos/lib/crtdll/mbstring/mbsstr.c
+++ b/reactos/lib/crtdll/mbstring/mbsstr.c
@@ -4,17 +4,17 @@
 unsigned char *_mbsstr(const unsigned char *src1,const unsigned char *src2)
 {
         int len;
- 
+
         if(src2 ==NULL || *src2 == 0)
-                return src1;  
-        
+                return (unsigned char *)src1;
+
         len = _mbstrlen(src2);
-                
-        while(*src1)  
-        {    
+
+        while(*src1)
+        {
                 if((*src1 == *src2) && (_mbsncmp(src1,src2,len) == 0))
-                        return(src1);    
-                src1 = (unsigned char *)_mbsinc(src1);  
-        } 
+                        return (unsigned char *)src1;
+                src1 = (unsigned char *)_mbsinc(src1);
+        }
         return NULL;
 }
\ No newline at end of file
diff --git a/reactos/lib/crtdll/mbstring/mbstrlen.c b/reactos/lib/crtdll/mbstring/mbstrlen.c
index 2a0e0ebc5f3..662595edafb 100644
--- a/reactos/lib/crtdll/mbstring/mbstrlen.c
+++ b/reactos/lib/crtdll/mbstring/mbstrlen.c
@@ -4,7 +4,8 @@
 size_t _mbstrlen( const char *string )
 {
 	char *s = (char *)string;
-	size_t i;
+	size_t i = 0;
+
 	while ( *s != 0 ) {
 		if ( _ismbblead(*s) )
 			s++;