学步园

#include <stdio.h>
#include <stdlib.h>
#include <ctype.h>
#include <assert.h>

#define MAX_LEN 1000000

static int f(int i);
static int index(int c);
void encrypt(char *str);
char str_buffer[MAX_LEN];

int main(int argc, char *argv[])
{
    while(scanf("%s", str_buffer) != EOF) {
        encrypt(str_buffer);
        printf("%s", str_buffer);
    }

    /*
    scanf("%s", str_buffer);
    encrypt(str_buffer);
    printf("%s", str_buffer);
    */

   return 0;
}


void encrypt(char *str) {
    //static char alphbelt[] = "ZabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXY";
    static char *alphbelt = "ZabcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXY";

    while(*str) {
        *str++ = alphbelt[index(*str)];
    }
}


static int index(int c){
    assert(isalpha(c));

    if(isupper(c)) {
       c = c - 'A' + 27;
    }else if(islower(c)){
       c = c - 'a' + 1;
    }else {
        printf("These is some non alphbet letter!\n");
        exit(1);
    }
    c = f(c) % 52;

    return c;
}

static int f(int i) {
    return i*i + i + 1;
}