题解 | #字符串加解密#

#include <stdio.h>
#include <ctype.h>
#include <string.h>

void encode(char *ptr)
{
    int len = strlen(ptr);
    for(int i = 0; i < len; i++)
    {
        if(isalpha(ptr[i]))
        {
            if(isupper(ptr[i]))
                ptr[i] = tolower(ptr[i]);
            else
                ptr[i] = toupper(ptr[i]);
            if('z' != tolower(ptr[i]))
                ptr[i]++;
            else
            {
                if(isupper(ptr[i]))
                    ptr[i] = 'A';
                else
                    ptr[i] = 'a';
            }
        }
        else if(isdigit(ptr[i]))
        {
            if('9' != ptr[i])
                ptr[i]++;
            else
                ptr[i] = '0';
        }
    }
}

void decode(char *ptr)
{
    int len = strlen(ptr);
    for(int i = 0; i < len; i++)
    {
        if(isalpha(ptr[i]))
        {
            if(isupper(ptr[i]))
                ptr[i] = tolower(ptr[i]);
            else
                ptr[i] = toupper(ptr[i]);
            if('a' != tolower(ptr[i]))
                ptr[i]--;
            else
            {
                if(isupper(ptr[i]))
                    ptr[i] = 'Z';
                else
                    ptr[i] = 'z';
            }
        }
        else if(isdigit(ptr[i]))
        {
            if('0' != ptr[i])
                ptr[i]--;
            else
                ptr[i] = '9';
        }
    }
}

int main(void)
{
    int i = 0;
    char str[512];
    while(gets(str))
    {
        if(i%2 == 0)
            encode(str);
        else
            decode(str);
        i++;
        printf("%s\n", str);
    }
    return 0;
}