题解 | 字符串加解密

#include <iostream>
#include <cctype>
using namespace std;

char alpha_trans(char c, bool decode) {
    char ans;
    if(isupper(c)) {
        int n = (c - 'A');
        if(!decode) n = (n + 1) % 26; //加密
        else n = (n + 25) % 26; //解密
        ans = n + 'A';
        ans = tolower(ans);
    } else {
        int n = (c - 'a');
        if(!decode) n = (n + 1) % 26; //加密
        else n = (n + 25) % 26; //解密
        ans = n + 'a';
        ans = toupper(ans);
    }
    return ans;
}

char num_trans(char c, bool decode) {
    int n = c - '0';
    if(decode) { //解密
        n = (n + 9) % 10;
    } else { //加密
        n = (n + 1) % 10;
    }
    c = '0' + n;
    return c;
}

int main() {
    string s, t;
    cin >> s >> t;
    string encrypt, decode;
    for(const char& c: s) { //对s加密
        if(isalpha(c)) {
            encrypt += alpha_trans(c, false);
        } else {
            encrypt += num_trans(c, false);
        }
    }
    for(const char& c: t) { //对t解密
        if(isalpha(c)) {
            decode += alpha_trans(c, true);
        } else {
            decode += num_trans(c, true);
        }
    }
    cout << encrypt << endl;
    cout << decode << endl;
    return 0;
}