把一个字符串的大写字母放到字符串的后面，各个字符的相对位置不变，不能申请额外的空间

#include<stdio.h>
#include<string.h>
char *Sort(char *str, int len)
{
     if(str==NULL || len<=0 )
        return NULL;
     char *start = str;
     int i = len - 1;
     int j = 0;
     int l = 0;
     for(; i>=0; i--)
     {
         if(str[i]>="A" && str[i]<="Z")
         {
             char t = str[i];
             int k = i;
             for(; k<len-1-l; k++)
                str[k] = str[k+1];
             str[k] = t;
             l++;
         }
     }
     return start;
}


int main()
{
    char s[] = "";//"aFkJmnVp";
    char *ret = Sort(s, strlen(s));
    if(ret!=NULL)
    {
        printf("%s
", ret);
    }
    else
    {
        printf("error!
");
    }
    return 0;
}