string.h

char* itoa(int n, char* str, int radix){
	
	char digit[] = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
	char* p = str;
	char* head = str;
	if(!p || radix<2 || radix >36)
	  return p;
	
	if(radix !=10 && n<0)
	  return p;

	if(n==0)
	{
	   *p++ = '0';
	   *p = 0;
	   return p;			
	}	
	
	if(radix ==10 && n<10)
	{
	   *p++ ='-';
	   n=-n;	
	}

	while(n)
	{
	   *p++ = digit[ n % radix];
	   n /= radix;
	}
	
	*p = 0;

	for(--p; head<p; ++head, --p)
	{
	   char temp = *head;
	   *head = *p;
	   *p = temp;
	}
	
	return str;
}

int strcmp( const char* src, const char*dst){

	int ret = 0;
	unsigned char* p1=(unsigned char*)src;
	unsigned char* p2=(unsigned char*)dst;
	while(! (ret = *p1 - *p2) && *p2)
	{
	   ++p1,++p2;
        }

	if(ret < 0)
	{
		ret = -1;
	}else if(ret > 0)
	      {
		ret = 1;
	      }
	  
        return ret;     	    
}

char *strcpy(char* dest, const char* src){

	char* ret = dest;
	while(*src)
	  *dest++= *src++;

	*dest ='\0';
	return ret;
}

unsigned strlen(const char* str){

	int cnt = 0;
	if(!str)
	  return 0;
	
	for(;*str!='\0';++str)
	{
	    ++cnt;	
	}

	return cnt;
}