66分求助，人要傻了，感谢回答

#include <stdio.h>
#include <string.h>
int max = 1000;

int main()
{
    char str[max];
    gets(str);
    int len = strlen(str);
    int diff = 'Z' - 'z';
    for (int i = 0; i<len;i++)//先大小写转换
    {
        if (str[i]<'z'&& str[i]>='a')
            str[i] = str[i]+diff;
        else 
            str[i] = str[i]-diff;
    }
    for (int i = 0;i<len;i++)//循环向左移三位
    {
        if ((str[i]<'x'&&str[i]>='a')||(str[i]<'X'&&str[i]>='A'))
            str[i] = str[i]+3;
        else
            str[i] = str[i]-23;
    }
    char outstr[len+1];
    for (int i = 0;i<len;i++)//逆序
    {
        outstr[i] = str[len-1-i];
    }
    outstr[len] = '\0'; 
    printf("%s",outstr);
    return 0;
}```