在string中删除start开始的length个字符，返回string.

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#define  MAX_LEN 100

char *strndel(char *str, int start, int length)
{
   char temp[MAX_LEN];
   int str_len = strlen(str);
   if ((start+length) > str_len)
       return NULL;
   strncpy(temp, str, start);
   temp[start] = '\0';
   strcat(temp, str+start+length);
   str = temp;
   printf("temp is  \n" );
   return str;
}

int main(void)
{
   char str[]="helloworld! I am Lau";
   printf("Result is %s \n", strndel(str, 3, 3));
   return 0；
}